The invention relates to several different areas and a discussion of some particular areas of interest follows. All mentioned patents, published patent applications and literature are incorporated by reference herein.
1. Crash Sensors
1.1 Pattern Recognition Approach to Crash Sensing
Pattern recognition techniques, such as artificial neural networks are finding increased application in solving a variety of problems such as optical character recognition, face recognition, voice recognition, and military target identification. In the automotive industry in particular, pattern recognition techniques are applied to identify various objects within the passenger compartment of the vehicle, such as a rear facing child seat, as well as to identify threatening objects with respect to the vehicle, such as an approaching vehicle about to impact the side of the vehicle (see, e.g., U.S. Pat. Nos. 5,829,782, 6,343,810 and U.S. RE37260).
Pattern recognition techniques are also applied to sense automobile crashes for the purpose of determining whether or not to deploy an airbag or other passive restraint, or to tighten the seatbelts, cutoff the fuel system, or unlock the doors after the crash (see, e.g., U.S. Pat. No. 5,684,701). In the past, pattern recognition techniques were not applied to forecast the severity of automobile crashes for the purpose of controlling the flow of gas into and/or out of an airbag to tailor the airbag inflation characteristics and/or to control seatbelt retractors, pretensioners and energy dissipaters to match the crash severity. Furthermore, such techniques were also not used to control the flow of gas into and/or out of an airbag to tailor the airbag inflation characteristics to the size, position and/or relative velocity of the occupant or other factors such as seatbelt usage, seat and seat back positions, headrest position, vehicle velocity, etc.
Neural networks are constructed of processing elements known as neurons that are interconnected using information channels often called interconnects organized into different layers. Each neuron can have multiple inputs but generally only one output. Each output however is usually connected to all other neurons in the next layer in the direction of processing. The neurons in the first layer operate collectively on the input data as described in more detail below. Neural networks learn by extracting relational information from the data and the desired output. Neural networks have been applied to a wide variety of pattern recognition problems including automobile occupant sensing, speech recognition, optical character recognition, and handwriting analysis.
1.2 Electronic Crash Sensors
Electronic crash sensors currently used in sensing frontal impacts typically include accelerometers mounted in the passenger compartment that detect and measure vehicle accelerations during the crash. The accelerometer produces an analog signal proportional to the acceleration experienced by the accelerometer and hence the vehicle on which it is mounted. An analog to digital converter (ADC) transforms this analog signal into a digital time series. Crash sensor designers study this digital acceleration data and derive therefrom computer algorithms which determine whether the acceleration data from a particular crash event warrants deployment of the airbag. This is usually a trial and error process wherein the engineer or crash sensor designer observes data from crashes where the airbag is desired and when it is not needed, and other events, such as rough road and abusive incidents, where the airbag is not needed. Finally, the engineer or crash sensor designer settles on the “rules” for controlling deployment of the airbag which are programmed into an algorithm which seem to satisfy the requirements of the crash library, i.e., the crash data accumulated from numerous crashes and other events and the associated desired restraint reaction. The resulting algorithm is not universal and most such engineers or crash sensor designers will answer in the negative when asked whether their algorithm will work for all vehicles. Such an algorithm also merely determines that the airbag should or should not be triggered. Prior to the current assignee's activities, no attempt is believed to have been made to ascertain or forecast the eventual severity of the crash or, more specifically, to forecast the velocity change versus time of the passenger compartment from the previous acceleration data obtained from the accelerometer.
Several papers as listed below have been published pointing out some of the problems and limitations of electronic crash sensors mounted out of the crush zone of the vehicle, usually in a protected location in the passenger compartment of the vehicle. These sensors are frequently called single point crash sensors. Technical papers which discuss the limitations of current single point sensors along with discussions of the theory of crash sensing are listed below. The only use of electronic sensors at the time of the filing of the current assignee's earliest parent patent application (U.S. Pat. No. 5,842,716 filed Sep. 16, 1993) was for non-crush zone sensing of frontal crashes. U.S. Pat. No. 3,701,903 shows crash sensors mounted near the front of the vehicle but it also points out that they are used “ . . . in response to changes in the vehicle's velocity” as opposed to the velocity change to a portion of the vehicle that undergoes crushing. Engineers involved in crash testing at that time were aware that in a crash test, it was common to lose one or more of the front crush zone mounted accelerometers and thus the prevailing wisdom was that the crush zone was not a place to position electronic sensors.
These papers demonstrate, among other things, that there is no known theory that allows an engineer to develop an algorithm for sensing crashes and selectively deploying the airbag except when the sensor is located in the crush zone of the vehicle. These papers show that, in general, there is insufficient information within the acceleration signal measured in the passenger compartment to sense all crashes. Another conclusion suggested by these technical papers is that if an algorithm can be found which works for one vehicle, it will also work for all vehicles since it is possible to create any crash pulse measured in one vehicle, in any vehicle. In this regard, reference is made to SAE paper 920124 discussed below.
In spite of the problems associated with finding the optimum crash sensor algorithm, many vehicles on the road today have electronic single point crash sensors. Some of the problems associated with single point sensors have the result that an out-of-position occupant who is sufficiently close to the airbag at the time of deployment will likely be injured or killed by the deployment itself. Fortunately, systems are now being developed, and are in limited production, that monitor the location of occupants within the vehicle and can suppress deployment of the airbag if the occupant is more likely to be injured by the deployment than by the accident. However, these systems are not believed to currently provide the information necessary for the control of airbag systems, or the combination of seatbelt and airbag systems, which have the capability of varying the flow of gas into and/or out of the airbag and thus to tailor the airbag to the size and/or weight of the occupant (and/or possibly another morphological characteristic of the occupant), as well as to the position, velocity and/or seatbelt use of the occupant. More particularly, no such system is believed to have existed, prior to the conception by the current assignee's personnel, which uses pattern recognition techniques to match the airbag deployment and/or gas discharge from the airbag to the severity of the crash and/or the size, weight, position, velocity and/or seatbelt use of an occupant.
Once any crash sensor has determined that an airbag should be deployed, the system can perform other functions such as tightening the seatbelts for those vehicles which have seatbelt retractor systems, cutting off of the fuel system to prevent fuel spillage during or after the crash, and unlocking the doors after the crash to make it easier for the occupant(s) to escape.
1.3 Crash Severity Prediction
When a crash commences, the vehicle starts decelerating and an accelerometer located in the passenger compartment, and/or one or more satellite or crush zone mounted accelerometers, begins sensing this deceleration and produces one or more electronic signals that vary over time in proportion to the magnitude of the deceleration. These signals contain information as to the type of the crash which can be used to identify the crash. A crash into a pole gives a different signal than a crash into a rigid barrier, for example, even during the early portion of the crash before the airbag triggering decision has been made. A neural network pattern recognition system can be trained to recognize and identify the crash type from the early signal from a passenger compartment mounted sensor, for example, and further to forecast ahead the velocity change versus time of the crash. If the neural network also has information from satellite or crush zone mounted sensors, the accuracy of the forecast is significantly improved. Once this forecast is made, the severity and timing of the crash can be predicted. Thus, for a rigid barrier impact, an estimate of the eventual velocity change of the crash can be made and the amount of gas needed in the airbag to cushion an occupant as well as the time available to direct that amount of gas into the airbag can be determined and used to control the airbag inflation.
Another example is a crash into a highway energy absorbing crash cushion. In this case, the neural-network-based sensor determines that this is a very slow crash and causes the airbag to inflate more slowly thereby reducing the incidence of collateral injuries such as broken arms and eye lacerations.
In both of these cases, the entire decision making process takes place before the airbag deployment is initiated. In another situation where a soft crash is preceded by a hard crash, such as might happen if a pole were in front of a barrier, the neural network system would first identify the soft pole crash and begin slowly inflating the airbag. However, once the barrier impact begins, the system would recognize that the crash type has changed and recalculate the amount and timing of the introduction of gas into the airbag and send appropriate commands to the inflation control system of the airbag to possibly vary the introduction of gas into the airbag. Again, if crush zone mounted sensors are present, the accuracy of the crash severity is greatly enhanced.
The use of pattern recognition techniques in crash sensors has another significant advantage in that it can share the same pattern recognition hardware and software with other systems in the vehicle. Pattern recognition techniques have proven effective in solving other problems related to airbag passive restraints. In particular, the identification of a rear-facing child seat located on the front passenger seat, so that the deployment of the airbag can be suppressed, has been demonstrated. Also, the use of pattern recognition techniques for the classification of vehicles about to impact the subject vehicle, particularly the side, for use in anticipatory crash sensing shows great promise. Both of these pattern recognition systems, as well as others under development, can use the same computer system as the crash sensor and prediction system of this invention. Moreover, both of these systems preferably will need to interact with, and should be part of, the diagnostic module used for frontal impacts. It would be desirable for cost and reliability considerations, therefore, for all such systems to use the same computer system or at least be located in the same electronic module. This is particularly desirable since computers designed specially for solving pattern recognition problems, such as neural-computers, are now available and can be integrated into a custom application specific integrated circuit (ASIC).
1.4 Crush Zone Mounted Sensors
In Society of Automotive Engineers (SAE) Paper No. 930650 entitled “A Complete Frontal Crash Sensor System”, the authors conclude that airbag crash sensors mounted in the crush zone are necessary for proper sensing of airbag-required frontal crashes. They also conclude that such sensors should sense crashes to all portions of the front of the vehicle and that sensors which sense the crush of the vehicle are preferred. The theory of crush sensing is presented in the above-referenced U.S. patents and patent applications and particularly in reference (6).
The tape switch and rod-in-tube crush sensors described in the above-referenced U.S. patents and patent applications have performed successfully on various staged vehicle frontal crashes into barriers and poles. These sensors are generally not sufficient for sensing side impacts as discussed in reference (11), however, they can be successful when used in conjunction with a passenger compartment mounted electronic sensor or as a safing sensor. Similarly, they are also being considered when a deployable device, such as an airbag, is used for rear impacts. Newer elongate crush zone mounted sensors are being developed that continuously measure the relative displacement, velocity change or acceleration of a particular location in the crush zone and therefore can give much improved information about the locating of an impact and the characteristics of the crash such as its severity.
Sensors have been widely used in the crush zone to sense and initiate deployment of an air bag passive restraint system. These sensors include an air damped ball-in-tube sensor such as disclosed in U.S. Pat. Nos. 3,974,350, 4,198,864, 4,284,863, 4,329,549 and 4,573,706 (all in the name of Breed) and a spring mass sensor such as disclosed in U.S. Pat. Nos. 4,116,132 and 4,167,276 (both in the name of Bell). In addition, a passenger compartment-mounted electronic sensor is now the most common sensor in airbag systems. Each of these sensors has particular advantages and shortcomings that are discussed in detail in U.S. Pat. No. 4,995,639.
The use of tape or ribbon switch technology as a crush switch was also disclosed in the '639 patent. Further research has shown that an improvement of this particular implementation has significant advantages over some of the other implementations since the switch can be easily made long and narrow and it can be made to respond to bending. In the first case, it can be designed to cover a significant distance across the vehicle that increases the probability that it will be struck by crushed material or bent as the crush zone propagates rearward in the vehicle during a crash. In the second case, it can be made small and located to sense the fact that one part of the vehicle has moved relative to some other part or that the structure on which the sensor is mounted has deformed.
Other crush zone mounted crash sensors including crush switch designs where the width and height dimensions are comparable, must either be large and thus heavy, expensive and difficult to mount, or there is a possibility that the randomly shaped crushed material which forms the boundary of the crush zone will bridge the sensor resulting in late triggering. This crushed material frequently contains holes, wrinkles or folds or portions that may even be displaced or torn out during the crash with the result that it is difficult to guarantee that a particular small area where the sensor is mounted will be struck early in the crash.
A significant improvement results, therefore, if the sensor can stretch across more of the vehicle or if it can determine that there has been relative motion or deformation of a portion of the vehicle on which the sensor is mounted. Some of the improved sensors described herein are small in height and thickness but can extend to whatever length is necessary to achieve a high probability of a sensor triggering on time in a crash.
It has been found that conventional designs of tape or ribbon switches have the drawback that the force required to close the switch is very small compared with the forces which are normally present in automobile crashes. During routine maintenance of the vehicle, the normal tape switch may be damaged or otherwise made to close and remain closed, with the result that later, when the vehicle encounters a pot hole or other shock sufficient to cause the arming sensor to close, an inadvertent air bag deployment can result. Similarly, if the tape switch is mounted on the front of the radiator support, which is a preferred mounting locating for crush zone sensors, hail, heavy rain, stones or other debris from the road might impact the tape switch and cause a momentary closure or damage it. If this happens when the vehicle experiences a shock sufficient to cause the arming sensor to close, an inadvertent air bag deployment might also occur. The force typically required to close a tape switch is less than one pound whereas tens of thousands of pounds are required to stop a vehicle in a crash and local forces greatly in excess of 20 pounds are usually available to actuate a sensor during a crash.
The present invention seeks to eliminate these drawbacks through the use of a tape switch, rod-in-tube or coaxial cable design that requires either a large force to actuate or a bending of the device due to structural deformation as explained below.
In 1992, the current assignee published reference (5) where the authors demonstrate that there is insufficient information in the non-crush zone of the vehicle to permit a decision to be made to deploy an airbag in time for many crashes. The crash sensors described herein and in the patents and patent applications referenced above, provide an apparatus and method for determining that the crush zone of the automobile has undergone a particular velocity change. This information can be used by itself to make the airbag deployment decision. As airbag systems become more sophisticated, however, the fact that the vehicle has undergone a velocity change in the crush zone can be used in conjunction with an electronic sensor mounted in the passenger compartment to not only determine that the airbag should be deployed but an assessment of the severity of the crash can be made. In this case, the front crush zone mounted sensor of the type disclosed herein can be used as an input to an electronic algorithm and thereby permit a deployment strategy based on the estimated severity of the accident. Although the sensors described herein are one preferred approach of providing this capability, the sensors disclosed in the above-referenced patents would also be suitable. Alternately, in some cases, sensors of another design can fulfill this function. Such sensors might be based on the electromechanical technologies such as the ball-in-tube sensor described in U.S. Pat. No. 4,900,880 and now electronic sensors can be used as crush zone mounted sensors for this purpose as is the object of the instant invention.
For the purposes herein, the crush zone is defined as that part of the vehicle which crushes or deforms during a particular crash. This is a different definition from that used elsewhere and in particular in the above-referenced technical papers. Also for the purposes herein, the terminology Crush Sensing Zone, or CSZ, will be used to designate that portion of the vehicle which is deformed or crushed during a crash at the sensor-required trigger time. The sensor-required trigger time is considered the latest time that a crash sensor can trigger for there to be sufficient time to deploy the airbag. This is determined by the airbag system designers and is a given parameter to the sensor designer for a particular crash. There will be a different sensor-required trigger time for each crash, however, it has been found, as reported in the above references, that the CSZ is remarkably constant for all crashes of the same type.
For example, the CSZ is nearly the same for all frontal barrier crashes regardless of the velocity of the crash. The same is true for 30 degree angle barrier crashes although the CSZ is different here than for frontal barrier crashes. Remarkably, and unexpectedly, it has also been found that when all frontal crashes at all different velocities are taken into account, the CSZ rearmost boundary becomes an approximate three dimensional surface lying mostly within the engine compartment of the vehicle, typically about ten to twelve inches behind the bumper at the center, and extending backward when crashes outside of the rails are considered. Finally, if a sensor is placed on this CSZ surface so that it is higher than the bumper level on the sides of the vehicle and lower in the vehicle center, as shown in FIG. 7 herein, it will do a remarkable job at discriminating between airbag deployment required and non-deployment crashes and still trigger by the sensor-required trigger time and before other sensors of comparable sensitivity. This system is not perfect, however, it has been shown to do a better job than any other sensor system now in use.
It was this discovery which provided a basis for the subject matter described in U.S. Pat. No. 4,995,639 and then to the rod-in-tube sensor described in U.S. Pat. No. 5,441,301. During the process of implementing the rod-in-tube sensor, it was found that the same theory applies to rear impacts and that rod-in-tube sensors also have applicability to side impact sensing primarily as safing or arming sensors.
In U.S. Pat. No. 5,694,320, the theory of sensing rear impacts is presented and it is concluded that an anticipatory sensing system is preferred. This is because many people suffer whiplash injuries at rather low velocity impacts and if an inflatable restraint is used, the repair cost may be significant. To protect most people from whiplash injuries in rear impacts, therefore, a resetable system is preferred. The argument on the other side is that if the headrest is properly positioned, it will take care of all of the low velocity impacts and, therefore, an airbag can be used and reserved for the high velocity impacts where a crush sensing crash sensor could be used. Rod-in-tube sensors disclosed herein are, therefore, ideal for use with a deployable headrest mounted airbag for the same reasons that it is a good sensor for sensing frontal impacts. Since the rear of a vehicle typically has about one third of the stiffness of the vehicle front, electronic sensors will have even a tougher time discriminating between trigger and non-trigger cases for rear impacts. As disclosed in references 5 and 9, it is the soft crashes that are the most difficult for electronic sensors to sense in time.
Crush sensing crash sensors are not ideal for sensing side impacts alone, although at least one Volvo side impact system uses such a sensing system. This is because the sensing time is so short that there is virtually no crush (about two inches) at the time that the airbag must be deployed. Since there is very little signal out of the crush zone where electronic sensors are mounted, electronic sensors alone are not able to discriminate airbag required crashes from other crashes not requiring airbag deployment. The combination of the two sensors, on the other hand, can be used to provide a reliable determination. The crush sensor determines that there has been two inches of crush and the electronic sensor determines that the acceleration signal at that time is consistent with an airbag-required crash occurring. Thus, although they cannot be reliably used alone as a discriminating sensor for side impacts, the combined system does function properly. Recent advances now permit electronic crash sensors to be mounted in the side as well as the front and rear crush zones.
An alternate use of the crush sensor such as the rod-in-tube sensor in side impacts is as a safing sensor. In this role, it merely determines that a crash is in progress and the main discriminating function is handled by the velocity sensing sensors such as disclosed in U.S. Pat. No. 5,231,253.
Rod-in-tube or coaxial cable crush velocity sensing crash sensors solve this side impact problem and thus applications include frontal, side and rear impacts, where in each case they enjoy significant advantages over all other crash sensing technologies. With respect to other related prior art, Peachey (U.S. Pat. No. 4,060,705) describes a pressure actuated continuous switch which designed to actuate about its entire circumference, i.e., in all directions. The switch of the embodiment in FIG. 1 of Peachey includes a central, inner conductor, an insulating thread helically wound around the conductor and an outer conductor, all housed within a sheath of insulating material. The switch in the embodiment of FIG. 2 includes a central, inner conductor, an insulating thread helically wound around the conductor, a sheath of graphite-loaded plastic surrounding the thread, an outer conductor surrounding the sheath and a sheath of insulating material surrounding the outer conductor. The switch in these embodiments is actuated when pressure is applied to the switch so that the outer conductor (FIG. 1) or sheath (FIG. 2) is deflected to cause it to make contact with the inner conductor and thereby establish electrical contact between the inner and outer conductors in the embodiment of FIG. 2 through the sheath. In view of the helical winding of the insulating thread around the inner conductor, these switches can be actuated by bending at almost all locations (except for an impact into a location where the insulating material is interposed between the conductors).
U.S. Pat. No. 2,437,969 to Paul describes a deformable switch in the form of a tube that is actuatable at all circumferential points along its length. The tube includes a central coil of electrically conducting wire, a braided electrically conducting, metal tube and insulating separators spaced at discrete locations along the length of the switch to support the tube around the wire. The switch is actuatable at all circumferential locations along the length of the tube, except for the locations at which the insulating separators 13 are located. In use, when pressure is applied to the tube, it deforms at the location at which pressure is applied thereby coming into contact with the wire and causing a circuit to close.
U.S. Pat. No. 5,322,323 to Ohno et al. describes to a collision sensing system for an airbag including collision sensors and acceleration sensors wherein deployment of the airbag is based on a signal from the collision sensors and an analysis of the output from the acceleration sensors.
U.S. Pat. No. 5,797,623 to Hubbard describes an allegedly unique side impact sensor based on a piezoelectric film. The sensor essentially measures the energy of impact providing the entire force applied to the film, which would not in general be the case. The velocity of the impacting vehicle can be determined again if the sensor absorbs the entire force and if the mass of the impacting object is known. Since neither of these can be assumed, the device will not provide a measurement of the impacting velocity and therefore at best can act as an impact-sensing switch with some discriminating capability.
The prior art crush zone mounted sensors therefore are either force sensing switches (Matsui) or piezoelectric film sensors (Hubbard) mounted in the forwardmost part of the crush zone, are velocity change sensors (ball-in-tube) mounted at the rear most edge of the CSZ or crush sensing switches also mounted at the rear most edge of the CSZ. Sensors mounted at the rearmost edge of the CSZ by nature will trigger at the last possible moment when the airbag must deploy based on the seating position of the average male occupant. It is known that currently up to about 70% of vehicle occupants sit closer to the airbag than the average male and therefore such sensors trigger airbag deployment late for such occupants placing them at risk of being injured by the airbag. Previously, there are no velocity change sensors that are mounted in the forward part of the crush zone where the velocity change of the crash can be determined early in the crash and the airbag deployed early. There is thus a need for such a crash sensor.
1.5 Side Impact Sensor Systems
Self-contained airbag systems contain all of the parts of the airbag system within a single package, in the case of mechanical implementations, and in the case of electrical or electronic systems, all parts except the primary source of electrical power and, in some cases, the diagnostic system. This includes the sensor, inflator and airbag. Potentially these systems have significant cost and reliability advantages over conventional systems where the sensor(s), diagnostic and backup power supply are mounted separate from the airbag module. In mechanical implementations in particular, all of the wiring, the diagnostic system and backup power supply are eliminated. In spite of these advantages, self-contained airbag systems have only achieved limited acceptance for frontal impacts and have so far not been considered for side impacts.
The “all-mechanical” self-contained systems were the first to appear on the market for frontal impacts but have not been widely adopted partially due to their sensitivity to accelerations in the vertical and lateral directions. These cross-axis accelerations have been shown to seriously degrade the performance of the most common all mechanical design that is disclosed in Thuen, U.S. Pat. No. 4,580,810. Both frontal and side impact crashes frequently have severe cross-axis accelerations.
Additionally, all-mechanical self-contained airbag systems, such as disclosed in the Thuen patent, require that the sensor be placed inside of the inflator which increases the strength requirements of the inflator walls and thus increases the size and weight of the system. One solution to this problem appears in Breed, U.S. Pat. No. 4,711,466, but has not been implemented. This patent discloses a method of initiating an inflator through the use of a percussion primer in combination with a stab primer and the placement of the sensor outside of the inflator. One disadvantage of this system is that a hole must still be placed in the inflator wall to accommodate the percussion primer that has its own housing. This hole weakens the wall of the inflator and also provides a potential path for gas to escape.
Another disadvantage in the Thuen system that makes it unusable for side impacts, is that the arming system is sealed from the environment by an O-ring. This sealing method may perform satisfactorily when the module is mounted in the protected passenger compartment but it would not be satisfactory for side impact cases where the module would be mounted in the vehicle door where it can be subjected to water, salt, dirt, and other harsh environments.
Self-contained electrical systems have also not been widely used. When airbags are used for both the driver and the passenger, self-contained airbag systems require a separate sensor and diagnostic for each module. In contrast to mechanical systems, the electronic sensor and diagnostic systems used by most vehicle manufacturers are expensive. This duplication and associated cost required for electrical systems eliminates some of the advantages of the self-contained system.
Sensors located in the passenger compartment of a vehicle can catch most airbag-required crashes for frontal impacts, particularly if the occupants are wearing seatbelts. However, researchers now believe that there are a significant number of crashes which cannot be sensed in time in the passenger compartment and that this will require the addition of another sensor mounted in the crush zone (see, e.g., reference 5). If true, this will eventually eliminate the use of self-contained airbag systems for frontal impacts.
Some of these problems do not apply to side impacts mainly because side impact sensors must trigger in a very few milliseconds when there is no significant signal at any point in the vehicle except where the car is crushing or at locations rigidly attached to this crush zone. Each airbag system must be mounted in the crush zone and generally will have its own sensor. Self-contained airbag systems have not been used previously for occupant protection for side impacts which is largely due to the misconception that side impact sensing requires the use of elongated switches as is discussed in detail in U.S. Pat. No. 5,231,253. These elongated prior art side impact crush-sensing switches are not readily adaptable to the more compact self-contained designs. The realization that a moving mass sensor was the proper method for sensing side impacts has now led to the development of the side impact self-contained airbag system of this invention. The theory of sensing side impacts is included in the '253 patent.
In electro-mechanical and electronic self-contained modules, the backup power supply and diagnostic system are frequently mounted apart from the airbag system. If a wire is severed during a crash but before the airbag deploys, the system may lose its power and fail to deploy. This is more likely to happen in a side impact where the wires must travel inside of the door. For this reason, mechanical self-contained systems have a significant reliability advantage over conventional electrical systems.
Finally, the space available for the mounting of airbag systems in the doors of vehicles is frequently severely limited making it desirable that the airbag module be as small as possible. Conventional gas generators use sodium azide as the gas generating propellant. This requires that the gas be cooled and extensively filtered to remove the sodium oxide, a toxic product of combustion. This is because the gas is exhausted into the passenger compartment where it can burn an occupant and is inhaled. If the gas is not permitted to enter the passenger compartment, the temperature of the gas can be higher and the products of combustion can contain toxic chemicals, such as carbon dioxide.
These and other problems associated with self-contained airbag systems and side impact sensors are solved by inventions disclosed herein.
1.6 Anticipatory Sensing
Although there has been a great deal of discussion on the use of anticipatory sensors for initiating restraint deployment, no practical systems have been developed other than those of the current assignee. The basic problem has been that an airbag should not be deployed unless the approaching object can be identified as a serious threat. The neural network systems developed by the current assignee is the first system capable of identifying such threatening objects.
1.7 Rollover Sensing
Various sensors exist for rollover sensing which detect the angular position of the vehicle.
1.8 Rear Impact Sensing
Various sensors exist for rear impact sensing which detect an impact into the rear of the vehicle.
1.9 Sensor Combinations
Up until the time that the first parent application was filed on this invention, it is believed that the only use of sensor combinations was where a discriminating sensor was in series with a safing or arming sensor and where a crush zone mounted discriminating sensor was in parallel with a passenger compartment discriminating sensor where either one could initiate deployment of the restraint system.
1.10 Safety Bus
It is not uncommon for an automotive vehicle today to have many motors, other actuators, lights etc., controlled by one hundred or more switches and fifty or more relays and connected together by almost five hundred meters of wire, and close to one thousand pin connections grouped in various numbers into connectors. It is not surprising therefore that the electrical system in a vehicle is by far the most unreliable system of the vehicle and the probable cause of most warranty repairs.
Unfortunately, the automobile industry is taking a piecemeal approach to solving this problem when a revolutionary approach is called for. Indeed, the current trend in the automotive industry is to group several devices of the vehicle's electrical system together which are located geometrically or physically in the same area of the vehicle and connect them to a zone module which is then connected by communication and power buses to the remainder of the vehicle's electrical system. The resulting hybrid systems still contain substantially the same number and assortment of connectors with only about a 20% reduction in the amount of wire in the vehicle.
Finally, the airbag electronics are generally housed separate and apart from the airbag module and the energy needed to initiate the inflator is transmitted to the airbag module after the crash sensor has determined that the airbag deployment is required. This has resulted in many failures of the airbag system due to shorted wires and other related causes. These and other problems could be solved if the crash sensor electronics send a coded signal to the airbag module and the electronics associated with the module decoded the signal to initiate the inflator.
The diagnostics circuitry can then also be part of or associated with the module along with the backup power supply which now also becomes the primary power supply for the module. This is sometimes known as the safety bus and there appears to be no prior art to the assignee's patents.
2. Inflators
2.1 Elongate Airbag Module
2.1.1 Ceiling Mounted
Devices are now being offered on vehicles that will monitor the position of the occupant and prevent the airbag from deploying if the occupant is dangerously close to the module where he or she can be seriously injured by the deployment. Some systems will also prevent deployment if the seat in connection with which the airbag operates is unoccupied. An alternate approach is to move the deployment doors to a location away from normal occupant positions. One such location is the ceiling of the vehicle. One problem with ceiling-mounted airbags is that the distance required for the airbag to travel, in some cases, is longer and therefore a larger airbag is needed with greater deployment time. With the use of light airbag materials, such as thin plastic film, as disclosed in U.S. Pat. Nos. 5,505,485 and 5,653,464, and the use of more efficient inflators, both of these problems can be solved especially for the front and rear seat passengers. The driver poses a different problem since it would be difficult to position a ceiling-mounted airbag module where the airbag would always be projected properly between the occupant and the steering wheel. On the other hand, the driver can usually ride down on the steering wheel if he or she is initially positioned close to it.
2.1.2 Steer by Wire
This problem for the driver's airbag system is not the concept of mounting the airbag on the ceiling, but the design of the steering wheel and steering column. These designs come from the time when the only way of steering an automobile was through mechanical linkages. The majority of vehicles manufactured today have power-assisted steering systems and, in fact, most drivers would have difficulty steering a car today if the power steering failed. If servo power steering were used, the need for a mechanical linkage between a steering wheel, or other such device, and the power steering system would no longer be necessary. Servo power steering for the purposes here will mean those cases where the linkage between the manually operated steering device, which regardless of what that device is, will herein be called a steering wheel, is done with a servo system either electrically or hydraulically and the system does not have an operative mechanical connection between the steering wheel and the steering mechanism which moves the wheels.
The problem of educating the general population, which has become secure in the feeling of a steering wheel and steering column, might be insurmountable if it were not for the substantial safety advantage resulting from substituting servo power steering for conventional steering systems and using a non-steering wheel mounted airbag module for the driver.
The steering wheel and steering column are among the most dangerous parts of the vehicle to the occupant. Small people, for example, who are wearing seatbelts can still be seriously injured or killed in accidents as their faces slam into steering wheel hubs. The problem of properly positioning an airbag, when the comfort and convenience features of telescoping and tilting steering columns are considered, results in substantial safety compromises. Deployment-induced injuries which result when a small person is close to the steering wheel when the airbag deploys have already caused several deaths and numerous serious injuries. Future vehicles, therefore, for safety reasons should be constructed without the massive steering wheel and steering column and substitute therefor a servo steering assembly. With this modification, a ceiling-mounted airbag module, such as discussed herein, becomes feasible for the driver as well as the other seating positions in the vehicle.
The front seat of the vehicle often has an airbag for the passenger and another for the driver. In some accidents, an occupant, and particularly a center-seated occupant, can pass between the two airbags and not receive the full protection from either one. If a ceiling-mounted airbag system were used, a single airbag could be deployed to cover the entire front seat greatly simplifying the airbag system design.
2.1.3 Mounted Rear-of-Seat
Other than disclosed in patents to the assignee, there appears not to be any prior art for rear of seat mounted airbags.
2.2 Aspirated Inflators
There are airbag modules in use which are relatively large, heavy, expensive and inefficient. As a result, airbags are now primarily only used for protecting the passenger and driver in a frontal impact, although most automobile manufacturers currently offer a small airbag providing limited protection in side impacts and many are now offering head protection or curtain airbags. The main advantage of airbags over other energy absorbing structures is that they utilize the space between the occupant and vehicle interior surfaces to absorb the kinetic energy of the occupant during a crash, cushioning the impending impact of the occupant with the vehicle interior surfaces. Airbags have been so successful in frontal impacts that it is only a matter of time before they are effectively used for side impact protection in all vehicles, protection for rear seat occupants and in place of current knee bolsters. Substantial improvements, however, must be made in airbags before they assume many of these additional tasks.
A good place to start describing the problems with current airbags is with a calculation of the amount of energy used in a typical airbag inflator and how much energy is required to inflate an airbag. By one analysis, the chemical propellant in a typical driver's side inflator contains approximately 50,000 foot pounds (68,000 joules) of energy. A calculation made to determine the energy required to inflate a driver's side airbag yields an estimate of about 500 foot pounds (680 joules). A comparison of these numbers shows that approximately 99% of the energy in a chemical propellant is lost, that is, generated but not needed for inflation of the airbag. One reason for this is that there is a mismatch between the output of a burning propellant and the inflation requirements of an airbag. In engineering this is known as an impedance mismatch. Stated simply, propellants naturally produce gases having high temperatures and high pressures and low gas flow rates. Airbags, on the other hand, need gases with low temperatures and low pressures and high gas flow rates.
In view of this impedance mismatch, inflators are, in theory at least, many times larger then they would have to be if the energy of the propellant contained within the inflator were efficiently utilized. Some attempts to partially solve this problem have resulted in a so-called “hybrid” inflator where a stored pressurized gas is heated by a propellant to inflate the airbag. Such systems are considerably more energy efficient, however, they also require a container of high pressure gas and monitoring of the pressure in that container. Other systems have attempted to use aspiration techniques, but because of the geometry constraints of current car inflator designs and mounting locations, and for other reasons, currently used aspiration systems are only able to draw significantly less than 30% of the gas needed to inflate an airbag from the passenger compartment. Theoretical studies and recent experiments have shown that as much as 90% or more of the gas could be obtained in this manner.
Furthermore, since inflators are large and inefficient, severe restrictions have been placed on the type of propellants that can be used since the combustion products of the propellant must be breathable by automobile occupants. It is of little value to save an occupant from death in an automobile accident only to suffocate him from an excessive amount of carbon dioxide in the air within the passenger compartment after the accident. If inflators operated more efficiently, then alternate, more efficient but slightly toxic propellants could be used. Also, most current inflators are made from propellants, namely sodium aside, which are not totally consumed. Only about 40% of the mass of sodium azide propellants currently being used, for example, enters the airbag as gas. This residual mass is very hot and requires the inflator to be mounted away from combustible materials further adding to the mass and size of the airbag system and restricts the materials that can be used for the inflator.
It is a persistent problem in the art that many people are being seriously injured or even killed today by the airbag itself. This generally happens when an occupant is out-of-position and against an airbag module when the airbag deploys. In order to open the module cover, sometimes called the deployment door, substantial pressure must first build up in the airbag before enough force is generated to burst open the cover. This pressure is even greater if the occupant is in a position that prevents the door from opening. As a result, work is underway to substantially reduce the amount of energy required to open the deployment doors and devices have been developed which pop off the deployment door or else cut the deployment door material using pyrotechnics, for example.
One reason that this is such a significant problem is that the airbag module itself is quite large and, in particular, the airbags are made out of thick, heavy material and packaged in a poor, folded geometry. The airbag, for example, which protects the passenger is housed in a module which is typically about one third as long as the deployed airbag. All of this heavy airbag material must be rolled and folded inside this comparatively small module, thus requiring substantial energy to unfold during deployment. This situation could be substantially improved if the airbag module were to have an alternate geometry and if the airbag material were substantially lighter and thinner and, therefore, less massive and folded mainly parallel to the inflator. Even the time to deploy the airbag is substantially affected by the mass of the airbag material and the need to unfold an airbag with a complicated folding pattern. Parallel folding, as used herein, means that the airbag material is folded with the fold lines substantially parallel to the axis of the inflator without being folded over lengthwise as is now done with conventional airbag folding patterns.
One method of partially solving many of these problems is to use an efficient aspirated airbag system. There have been numerous patents granted on designs for airbag systems using aspirated inflators. In these patents as well as in the discussion herein the term “pumping ratio” is used. The pumping ratio as used in the art is defined as the ratio of the mass of gas aspirated from the environment, either from inside or outside of the vehicle, to the mass of gas generated by burning the propellant. An alternate definition is the ratio of the total gas in the airbag to the gas produced by the propellant. A brief description of several pertinent aspiration patents follows:
U.S. Pat. No. 2,052,869 to Coanda shows the manner in which a fluid jet is caused to change direction, although no mention is made of its use in airbags. This principle, the “Coanda effect”, is used in some implementations of the instant invention as well as in U.S. Pat. No. 3,909,037 to Stewart discussed below. Its primary contribution is that when used in inflator designs, it permits a reduction in the length of the nozzle required to efficiently aspirate air into the airbag. No disclosure is made of a pumping ratio in this system and in fact it is not an object of Coanda to aspirate fluid.
U.S. Pat. No. 3,204,862 to Hadeler predates vehicular airbags but is nonetheless a good example of the use of aspiration to inflate an inflatable structure. In this device, an inflating gas is injected into an annular converging-diverging nozzle and some space efficiency is obtained by locating the nozzle so that the flow is parallel to the wall of the inflatable structure. No mention is made of a pumping ratio of this device and furthermore, this device is circular.
U.S. Pat. No. 3,632,133 to Hass provides a good example of a nozzle in a circular module with a high pumping ratio in an early construction of an airbag. Although analysis indicates that pumping ratios of 4:1 or 5:1 would be difficult to achieve with this design as illustrated, nevertheless, this reference illustrates the size and rough shape of an aspirating system which is required to obtain high pumping ratios using the prior art designs.
U.S. Pat. No. 3,909,037 to Stewart provides a good example of the application of the Coanda effect to airbag aspirating inflators. Stewart, nevertheless, still discards most of the energy in the propellant which is absorbed as heat in the inflator mechanism. Most propellants considered for airbag applications burn at pressures in excess of about 1000 psig. Stewart discloses that the maximum efficiency corresponding to a 5:1 pumping ratio occurs at inflator gas pressures of about 5-45 psig. In order to reduce the pressure, Stewart utilizes a complicated filtering system similar to that used in conventional inflators. Stewart requires the use of valves to close off the aspiration ports when the system is not aspirating. Through the use of the Coanda effect, Stewart alludes to a substantial reduction in the size of the aspiration system, compared to Hass for example. Also, Stewart shows only a simple converging nozzle through which the burning propellant is passed.
U.S. Pat. No. 4,833,996 to Hayashi et al. describes a gas generating apparatus for inflating an airbag which is circular and allegedly provides an instantaneous pumping ratio of up to 7:1 although analysis shows that this is unlikely in the illustrated geometry. The average pumping ratio is specified to be up to 4:1. This invention is designed for the driver side of the vehicle where unrestricted access to the aspirating port might be difficult to achieve when mounted on a steering wheel. The propellant of choice in Hayashi et al. is sodium azide which requires extensive filtering to remove particulates. No attempt has been made in this design to optimize the nozzle geometry to make use of a converging-diverging nozzle design, for example. Also, the inflator has a roughly conventional driver side shape. It is also interesting to note that no mention is made of valves to close off or restrict flow through the aspiration port during deflation. Since most aspiration designs having even substantially smaller pumping ratios provide for such valves, the elimination of these valves would be a significant advance in the art. Analysis shows, however, that the opening needed for the claimed aspiration ratios would in general be far too large for it also to be used for exhausting the airbag during a crash.
U.S. Pat. No. 4,877,264 to Cuevas describes an aspirating/venting airbag module assembly which includes a circular gas generator and contemplates the use of conventional sodium aside propellants or equivalent. The aspiration or pumping ratio of this inflator is approximately 0.2:1, substantially below that of Hayashi et al., but more in line with aspiration systems in common use today. This design also does not require use of aspiration valves which is more reasonable for this case, but still unlikely, since the aspiration port area is much smaller. No attempt has been made to optimize the nozzle design as is evident by the short nozzle length and the low pumping ratio.
U.S. Pat. No. 4,909,549 to Poole et al. describes a process for inflating an airbag with an aspiration system but does not discuss the aspiration design or mechanism and merely asserts that a ratio as high as 4:1 is possible but assumes that 2.5:1 is available. This patent is significant in that it discloses the idea that if such high pumping ratios are obtainable (i.e., 2.5:1 compared with 0.2:1 for inflators in use), then certain propellants, which would otherwise be unacceptable due to their production of toxic chemicals, can be used. For example, the patent discloses the use of tetrazol compounds. It is interesting to note that there as yet is no commercialization of the Poole et al. invention which raises the question as to whether such high aspiration ratios are in fact achievable with any of the prior art designs. Analysis has shown that this is the case, that is, that such large aspiration ratios are not achievable with the prior art designs.
U.S. Pat. No. 4,928,991 to Thom describes an aspirating inflator assembly including aspiration valves which are generally needed in all high pumping ratio aspiration systems. Sodium azide is the propellant used. Pumping ratios of 1:1 to 1.5:1 are mentioned in this patent which by analysis is possible. It is noteworthy that the preamble of this patent discloses that the state of the art of aspirating inflators yields pumping ratios of 0.1:1 to 0.5:1, far below those specified in several of the above referenced earlier patents. Little attempt has been made to optimize the nozzle design.
U.S. Pat. No. 5,004,586 to Hayashi et al. describes a sodium azide driver side inflator in which the aspirating air flows through a series of annular slots on the circumference of the circular inflator in contrast to the earlier Hayashi et al. patent where the flow was on the axis. Similar pumping ratios of about 4:1 are claimed however, which by analysis is unlikely. Once again, aspiration valves are not shown and the reason that they can be neglected is not discussed. An inefficient nozzle design is again illustrated. The lack of commercial success of these two Hayashi patents is probably due to the fact that such high pumping ratios as claimed are not in fact achievable in the geometries illustrated.
U.S. Pat. No. 5,060,973 to Giovanetti describes a liquid propellant airbag gas generator wherein the propellant burns clean and does not require filters to trap solid particles. Thus, it is one preferred propellant for use in the instant invention. This system however produces a gas which is too hot for use directly to inflate an airbag. The gas also contains substantial quantities of steam as well as carbon dioxide. The steam can cause burns to occupants and carbon dioxide in significant quantities is toxic. The gas generator is also circular. Aspirating systems are therefore required when using the liquid propellant disclosed in this patent, or alternately, the gas generated must be exhausted outside of the vehicle.
U.S. Pat. No. 5,129,674 to Levosinski describes a converging-diverging nozzle design which provides for more efficient aspiration than some of the above discussed patents. Nevertheless, the airbag system disclosed is quite large and limited in length such that the flow passageways are quite large which requires a long nozzle design for efficient operation. Since there is insufficient space for a long nozzle, it can be estimated that this system has a pumping ratio less than 1:1 and probably less than 0.2:1. Once again, a sodium azide based propellant is used.
U.S. Pat. No. 5,207,450 to Pack, Jr. et al. describes an aspirated air cushion restraint system in which no attempt was made to optimize the nozzle design for this sodium azide driver side airbag. Also, aspiration valves are used although it is suggested that the exhaust from the airbag can be made through the aspirating holes thereby eliminating the need for the flapper valves. No analysis, however, is provided to prove that the area of the aspiration holes is comparable to the area of the exhaust holes normally provided in the airbag. Although no mention is made of the pumping ratio of this design, the device as illustrated appears to be approximately the same size as a conventional driver side inflator. This, coupled with an analysis of the geometry, indicates a pumping ratio of less than 1:1 and probably less than 0.2:1. The statement that the aspiration valves are not needed also indicates that the aspiration ratio must be small. Large inlet ports which are needed for large aspiration ratios are generally much larger than the typical airbag exhaust ports.
U.S. Pat. No. 5,286,054 to Cuevas describes an aspirating/venting motor vehicle passenger airbag module in which the principal of operation is similar to the '264 patent discussed above. The aspiration pumping ratio of this device is 0.15:1 to 0.2:1 which is in line with conventional aspirated inflators. It is interesting to note that this pioneer in the field does not avail himself of designs purporting to yield higher pumping ratios. The nozzle design has not been optimized.
U.S. Pat. No. 6,062,143 to Grace et al. describes a distributed charge inflator system including a distributed gas-generating material having a faster burning center core ignition material surrounded by supplemental propellant, and an initiator to ignite the gas generating material upon a signal from an initiating device. A homogeneous mixture of ignition material and propellant is also described.
Other U.S. patents which are relevant to the instant invention but which will not be discussed in detail are: U.S. Pat. No. 3,158,314 to Young et al., U.S. Pat. No. 3,370,784 to Day, U.S. Pat. No. 5,085,465 to Hieahim, U.S. Pat. No. 5,100,172 to Van Voorhies et al., U.S. Pat. No. 5,193,847 to Nakayama, U.S. Pat. No. 5,332,259 to Conlee et al. and U.S. Pat. No. 5,423,571 to Hawthorn.
None of the prior art inflators are believed to contain the advantages of the combination of (i) a linear inflator having a small cross section thereby permitting an efficient nozzle design wherein the length of the nozzle is much greater than the aspiration port opening, (ii) a non sodium aside propellant which may produce toxic gas if not diluted with substantial quantities of ambient air, and (iii) an inflator where minimal or no filtering or heat absorption is required.
It is interesting to note that in spite of the large aspiration pumping ratios mentioned and even claimed in the prior art mentioned above, and to the very significant advantages which would result if such ratios could be achieved, none has been successfully adapted to an automobile airbag system. One reason may be that pumping ratios which are achievable in a steady state laboratory environment are more difficult to achieve in the transient conditions of an actual airbag deployment.
None of these prior art designs has resulted in a thin linear module which permits the space necessary for an efficient nozzle design as disclosed herein. In spite of the many advantages claimed in the prior art patents, none have resulted in a module which can be mounted within the vehicle headliner trim, for example, or can be made to conform to a curved surface. In fact, the rigid shape of conventional airbag modules has forced the vehicle interior designers to compromise their designs since the surface of such modules must be a substantially flat plane.
With respect to airbag systems including a plurality of inflatable airbags or unconventionally large airbags and inflators therefor, automobile manufacturers are now installing more than two airbags into a vehicle. The placement of both side and rear seat airbags have in fact taken place. Nissan for example has installed some rear airbags. Most automobile manufacturers are now installing side airbags. However, Nissan has stated that it cannot provide more than a total of two airbags in the vehicle and that it will not offer a front passenger side airbag for those vehicles that have a rear seat airbag. Side airbags will generally not deploy when the frontal airbags do because if more than two airbags would be deployed in a vehicle at the same time, the pressure generated by the deploying airbags within the passenger compartment of the vehicle creates large forces on the doors. These forces may be sufficient to force the doors open and consequently, if the doors of the vehicle are forced open during a crash, vehicle occupants might be ejected, greatly increasing the likelihood of serious injury. In addition, the pressure generated within the passenger compartment creates excessive noise which can injure human beings.
In addition to airbags for side impacts and rear seats, it is likely that airbags will be used as knee bolsters since automobile manufacturers are having serious problems protecting knees from injury in crashes while providing the comfort space desired by their customers.
As soon as three or more non-aspirated airbags are deployed in an accident, provisions should be made to open a hole in the vehicle to permit the pressure generated by the deploying airbags to escape. What has not been appreciated, however, is that once there is a significant opening from the vehicle to the outside, the requirements for the composition of the inflator gases used to inflate the airbags change and inflators which generate a significant amount of toxic gas become feasible, as will be discussed below.
The primary gas generating propellant used in airbag systems is sodium aside. This is partially due to the fact that when sodium aside burns, in the presence of an oxidizer, it produces large amounts of Nitrogen gas. It also produces sodium oxide which must be retained in the inflator since sodium oxide, when mixed with moisture, becomes lye and is very toxic to humans. Thus, current inflators emit only nitrogen gas into the passenger compartment which occupants can breath for a long period of time in a closed passenger compartment without danger. The sodium azide inflators also are large to accommodate the fact that about 60% of the gas generating material remains in the inflator with only about 40% emerging as gas.
Other propellants, including nitrocellulose, nitroguanidine, and other double base and triple base formulations, as well as a large number of liquid propellants, exist which could be used to inflate airbags, however they usually produce various quantities of gases containing compounds of nitrogen and oxygen plus significant amounts of carbon dioxide. In many cases, the gases produced by these other propellants are only toxic to humans if breathed over an extended period of time. If the toxic gas were removed from the vehicle within a few minutes after the accident, then many of these propellants would be usable to inflate airbags.
Much of the energy released when sodium azide burns in the inflator is removed from the gas by the cooling and filtering screens. In some designs, the sodium oxide must be trapped by the filters, which requires that the gas be cooled to the point where sodium oxide condenses. In all designs, the gas is cooled so that the temperature of the gas in the airbag will not cause burns to the occupants. It is believed that in all current designs, a substantial amount of the energy in a propellant is lost through this cooling process which in turn necessitates that the inflator contains more propellant.
Airbag systems have primarily been installed within the instrument panel or steering wheel of automobiles. As a result, although numerous attempts have been made to create aspirated inflator systems, they have only been used on the passenger side and their efficiency has been low. In aspirated inflator systems, part of the gas to inflate the airbag is drawn in from the passenger compartment. However, in a typical passenger side airbag system in use where aspiration is employed, substantially less than about 30% of the gas which inflates the airbag comes from the passenger compartment and some researchers state that it is even below about 5%. In view of the large size of conventional sodium azide inflators and woven airbags, there is limited room for the airbag system and it is difficult to design aspirating systems which will fit within the remaining available space. One reason is the resistance of the air flow through the instrument panel into the aspirator. Another reason for the low efficiency of aspirated inflator systems is that the aspirated systems used typically have inefficient nozzle designs. Theoretical studies of aspiration systems, such as described herein, show that the percentage of gas drawn in from the passenger compartment could be raised to as high as about 75% or even 90%.
As mentioned above, one airbag aspiration method is described in U.S. Pat. No. 4,909,549 to Poole et al. Poole et al. describes a method for inflating an airbag in which a substantially non-toxic primary gas mixture is diluted with outside air by passing the primary gas mixture through a venturi to aspirate the air. Poole et al. does not suggest that the outside air should come from the passenger compartment and therefore does not provide a solution to the problem of excessive pressure being generated in the passenger compartment upon deployment of multiple airbags, as discussed above.
If alternate, more efficient propellants are used and if the gas produced thereby is exhausted at a much higher temperature, more of the energy would be available to heat the gas which is flowing from the passenger compartment to the airbag thus further increasing the efficiency of the system and reducing the amount of propellant required. Since cooling screens are not necessary and since the efficiency of the propellant is high, the inflator can be made very small providing the extra space needed to design efficient aspirating nozzles.
Since many alternate propellants produce toxic gases, their use becomes practical (i) if the quantity used is substantially reduced, (ii) if means are provided to prevent the gas from entering the occupant compartment, and/or (iii) if means exist within the vehicle to exhaust the toxic gas from the vehicle shortly after the airbag is deployed.
2.2.1 Plastic Inflator
There appears to be no related art suggesting the use of plastic for an inflator housing.
2.2.2 Vary Burn Rate
There appears to be no related art to an arbitrary control of the rate of burning of the inflator propellant through variation in the cross-sectional shape of the propellant and thus its burning rate, although there is discussion in several references that the burn rate is proportional to the surface area that is burning.
2.2.3 Liquid Propellant
There appears to be no related art suggesting the use of a liquid propellant with as aspirated inflator design.
2.2.4 Propellant Considerations
There appears to be little related art suggesting that slightly toxic propellants can be used with an aspirated inflator.
2.2.5 Cover Considerations
There appears to be no related art suggesting how an airbag cover can be efficiently removed from an elongated airbag module having an aspirated inflator.
2.3 Controlling Amount of Gas in the Airbag
The amount of gas in an airbag can be controlled by controlling the rate that the inflator produces gas, the amount of the produced gas that actually enters the airbag and/or the outflow of the gas from the airbag.
2.3.1 Production of Gas
Primitive control of the production of the gas production first appeared in U.S. Pat. No. 4,380,346 where different thickness foils are placed over various exit orifices such that the flow is restricted from exiting the inflator until the pressure reached the design value. U.S. Pat. No. 5,772,238 is an early disclosure of the concept of varying the size of an exit orifice as a function of the pressure within the inflator to control the mass flow of gas out of the inflator. Subsequent patents including U.S. Pat. Nos. 5,951,040, 5,984,352, 6,142,515, 6,227,565, 6,290,256, 6,314,889, 6,315,322, 6,543,805, 6,655,712, 6,702,323 and US published Pat. Application 2004/0145166 have further developed this flow control principle. Of particular interest are U.S. Pat. No. 6,314,889 and US published Pat. Application 2004/0145166 which discuss the variation in the flow based on the measurement of “at least one chosen product gas performance factor.”
2.3.2 Control Module
U.S. Pat. No. 6,532,408 is an early disclosure of a control module designed to control the inflow and outflow of gas from an airbag which implies that any such method including variable control of inflator gas production is considered. Such a control module takes into account such factors as seat occupancy, classification of the seat occupant, position or the seat occupant, severity of the crash etc. Some of these features were later discussed in U.S. Pat. No. 6,314,889 and US published Pat. Application 2004/0145166.
2.3.3 Control of Gas Outflow
See section 3.8.
2.4 Exhausting Inflator Gas
2.4.1 Removing Window
There appears to be no related art suggesting the intention breaking of a window to allow a path for the excess pressure created when many airbags are deployed and when there is toxic gas emitted.
2.4.2 Exhaust Airbag from Vehicle
There appears to be little related art suggesting the exhausting of the inflator gases outside of the passenger compartment.
2.4.3 Blow Out Panel
There appears to be no related art suggesting the exhausting of the inflator gases outside of the passenger compartment through the use of a blow out panel.
2.4.4 Exhaust Fan
There appears to be no related art suggesting the exhausting of the inflator gases outside of the passenger compartment through the use of an exhaust fan.
3 Airbags
3.1 Plastic Film Airbags
Plastic films have not previously been used to make airbags with the exception of perforated films as disclosed in U.S. Pat. No. 4,963,412 to Kokeguchi, which is discussed below.
U.S. Pat. No. 3,451,693 (Carey) describes the presence of a variable exhaust orifice in an airbag which maintains constant pressure in the airbag as the occupant is thrown into the airbag but does not disclose plastic film, merely plastic. The distinguishable properties of film are numerically described in the instant specification and basically are thinner and less weight. The material of Carey is not plastic film which is capable of arresting the propagation of a tear. In fact, it is unclear in Carey as to whether the orifice can be varied in a repeatable/reusable manner and no mention is made as to whether the stretching of the orifice area is permanent or temporary.
U.S. Pat. No. 5,811,506 (Slagel) describes a thermoplastic, elastomeric polyurethane for use in making vehicular airbags. The polyurethane is extrudable so that airbags of various shapes and sizes can be formed therefrom.
U.S. Pat. No. 6,627,275 (Chen) describes the use of crystal gels to achieve tear resistance for airbags. This is a particular example of the teachings herein for the use of the thermoplastic elastomers to achieve tear resistance through the use of a particular subclass of such polymers. No mention is made, however, to laminate these materials with a film with a higher elastic modulus as is taught herein. Although interesting materials, they may not be practical for airbags due to their high cost. In particular, the crystal gel described in Chen is part of a class of thermoplastic elastomer (TPE) and in particular of polyester elastomers such as HYTREL™ which are discussed elsewhere herein and in the parent applications listed above. It is important to note that the particular formulations listed in Chen are probably poor choices for the blunting film portion of a laminated film used to make film airbags. This is due to their very high elasticity of 104 to 106 dynes per cm2 (see Chen at col. 21, line 4). This corresponds to the liquid crystal polymers which have an elastic modulus of above 1010 dynes per cm2. Thus, they will provide little resistance to the propagation of a tear in the higher modulus component of the laminated film and would be poor as the blunting layer.
It is important to note that liquid crystal polymers of a different sort than disclosed in Chen having quite the opposite properties would be ideal candidates for the high modulus component of a laminated film due to their inelastic nature, that is their high modulus of elasticity. Although these materials are considerably more expensive than NYLON®, for example, they are about twice as strong and therefore only half as much would be required. This would render the inner layer, for example, of a lamination with perhaps urethane as the outer layers, half the thickness and thus one eighth of the bending stiffness of NYLON®. Thus, the laminated airbag made in this manner would be considerably easier to fold and when folded, it would occupy substantially less space.
Another advantage of the more rigid liquid crystal polymers is that they can be laminated to polyurethane or other blunting materials without the need for an adhesive. This results in a significant cost saving for the laminated film and thus partially offsets the higher cost of the material compared with NYLON®, for example. Naturally, they can also be laminated to a more elastic liquid crystal polymer.
Note also that the “soft, safe, hugging, enveloping inflatable restraint cushions” described in Chen are not applicable in the form disclosed because, if used in a thin film version, it would blow up like a balloon permitting the occupant to easily displace the gas and penetrate far into the airbag. If used in a thick film version so that it does not stretch, then the advantages of the material are lost and the airbag would be similar in weight to a fabric airbag. However, if it is laminated to a more rigid material or a net as disclosed herein and in the previous patents of the current assignee, then again many of the advantages of the material are lost since the main material providing the strength to the airbag is the more rigid film or net layer. Nevertheless, providing there is not too much of a cost penalty the “elastic-crystalline gels” described in Chen might be advantageously used in the inventions described herein for some applications. Some other patents assigned to the same assignee as Chen that may be relevant to inventions herein are: U.S. Pat. Nos. 6,552,109, 6,420,475, 6,333,374 6,324,703, 6,148,830, 6,117,176, 6,050,871, 5,962,572, 5,884,639, 5,868,597, 5,760,117, 5,655,947, 5,633,286, 5,508,334, 5,336,708, 5,334,646, 5,324,222, 5,262,468 and 4,369,284.
Although airbags are now installed in all new vehicles and each year an increasing number of airbags are making their way into new vehicle designs, they are still basically the same design as originally invented about 40 years ago. Generally, each driver and passenger side airbag is a single chamber or at most two chambers, they are made from fabric that has sufficient mass as to cause injury to an occupant that is in the deployment path and they are positioned so that a forward-facing occupant will be protected in a substantially frontal impact. In contrast, many occupants are out-of-position and many real world crashes involved highly angular impacts, spinouts, rollovers etc. where the occupant is frequently injured by the deploying airbag and impacts other objects in the vehicle compartment in addition to the airbag.
In the out-of-position case, occupant sensors are now being considered to prevent or control the deployment of the airbag to minimize deployment induced injuries. These occupant sensors will significantly reduce the number of deaths caused by airbags but in doing so, they can deprive the occupant of the protection afforded by a softer airbag if the deployment is suppressed. Side and side curtain airbags are being installed to give additional protection to occupants in side impacts and rollovers. However, there still will be many situations where occupants will continue to be injured in crashes where airbags could have been a significant aid. What is needed is an airbag system that totally surrounds the occupant and holds him or her in the position that he or she is prior to the crash. The airbag system needs to deploy very rapidly, contact the occupant without causing injury and prevent his or her motion until the crash is over. This is a system that fills up the passenger compartment in substantially the same way that packaging material is used to prevent breakage of a crystal glass during shipment.
To accomplish this self-adjusting airbag system, the airbags must be made of very light material so that when they impact the occupant, they do not cause injury. They also must be inflated largely with the gas that is in the passenger compartment or else serious ear injuries may result and the doors and windows may be blown out. Thus, an airbag system comprised of many mini-airbags all connected together and inflated with one or more aspirated inflators that limit the pressure within each mini-airbag is needed. This is one focus of this invention. As it is accomplished, the inflators will get smaller and simpler since there will be no need for dual stage inflators. Since out-of-position occupants will not be injured by the deploying airbags, there will be no need for occupant sensors and children can safely ride in the front seat of a vehicle. The entire system will deploy regardless of the direction of the impact and the occupants will be frozen in their pre-crash positions until the crash is over.
Anticipatory crash sensors based on pattern recognition technology are disclosed in several of current assignee's patents and pending patent applications (see, e.g., U.S. Pat. Nos. 6,343,810, 6,209,909, 6,623,033, 6,746,078 and US20020166710). The technology now exists to allow the identification and relative velocity determination to be made for any airbag-required accident prior to the accident occurring (anticipatory sensing). This achievement now allows airbags to be reliably deployed prior to the accident. The implications of this are significant. Prior to this achievement, the airbag system had to wait until an accident started before a determination could be made whether to deploy the airbags. The result is that the occupants, especially if unbelted, would frequently achieve a significant velocity relative to the vehicle passenger compartment before the airbags began to interact with the occupant and reduce his or her relative velocity. This would frequently subject the occupant to high accelerations, in some cases in excess of 40 Gs, and in many cases result in serious injury or death to the occupant. On the other hand, a vehicle typically undergoes less than a maximum of 20 Gs during even the most severe crashes. Most occupants can withstand 20 Gs with little or no injury. Thus, as taught herein, if the accident severity could be forecast prior to impact and the vehicle filled with plastic film airbags that freeze the occupants in their pre-crash positions, many lives could be saved and many injuries avoided.
A main argument against anticipatory sensors is that the mass of the impacting object remains unknown until the accident commences. However, through using a camera, or other imaging technology based on, e.g., infrared, radar or terahertz generators and receivers, to monitor potentially impacting objects and pattern recognition technologies such as neural networks, the object can be identified and in the case of another vehicle, the mass of the vehicle when it is in the unloaded condition can be found from a stored table in the vehicle system. If the vehicle is a commercial truck, then whether it is loaded or not will have little effect on the severity of an accident. Also if the relative velocity of the impacting vehicles is above some threshold, then again the mass of the impacting vehicle is not important to the deployment decision. Pickup trucks and vans are thus the main concern because as loaded, they can perhaps weigh 50 percent more than when unloaded. However, such vehicles are usually within 10% of their unloaded-plus-one-passenger weight almost all of the time. Since the decision to be made is whether or not to deploy the airbag, in all severe cases and most marginal cases, the correct decision will be made to deploy the airbag regardless if there is additional weight in the vehicle. If the assumption is made that such vehicles are loaded with no more than 10% additional weight, then only in a few marginal crashes, a no-deployment decision will be made when a deployment decision is correct. However, as soon as the accident commences, the traditional crash sensors will detect the accident and deploy the airbags, but for those marginal cases the occupants will have obtained little relative forward velocity anyway and probably not be hurt and certainly not killed by the deploying plastic film airbags which stop deploying as soon as the occupant is contacted. Thus, the combination of anticipatory sensor technology and plastic film airbags as disclosed herein results in the next generation self adapting safety system that maximizes occupant protection. Both technologies preferably can be used together.
Another feature of plastic film airbags discussed below is the ability of film to be easily joined together to form structures that would be difficult or impossible to achieve with fabric such as the addition of a sheet of film to span the chambers of a side curtain airbag. It is well known that side curtain airbags are formed with chambers in order to limit the thickness of the curtain. This results in a curtain with reduced stiffness to resist the impact of the head of an occupant, for example, and to also form areas where the protection is less than other areas due to the presence of seams. Using film, these seam sections can be easily spanned without running the risk of introducing additional leakage paths in the airbag. This spanning of the chambers can produce additional chambers that can also be pressurized or the additional chambers can be left open to the atmosphere.
An analysis of a driver airbag made from two flat sheets of inelastic film shows that maximum stresses occur in the center of the airbag where the curvature is at a minimum. Thus, the material strength and not the seal or seam strength limits the pressure that causes the airbag to fail. On the other hand, analysis of some conventional side curtain airbags has shown that maximum stress can occur in the seams and thus the maximum pressure that the airbag can hold without bursting is limited by the material strength in the seams. This fact is at least partially the cause of excessive gas leakage at the seams of some fabric airbags necessitating the lamination of a polymer film onto the outside of the airbag. This problem is even more evident when the bag is made by continuous weaving where the chambers are formed by weaving two sheets of material together. A solution to this problem as discussed below is to first optimize the design of the seam area to reduce stresses and then to form the airbag by joining the sheets of material by heat sealing, for example, where an elastic material forms the seam that joins the sheets together. Such a joint permits the material to stretch and smooth the stresses, eliminating the stress concentrations and again placing the maximum stresses in the material at locations away from the seam. This has the overall effect of permitting the airbag to be constructed from thinner material permitting a more rapid deployment and causing less injury to an out-of-position occupant. This technique also facilitates the use of plastic film as an airbag material. Such a film can comprise a relatively inelastic, biaxially oriented layer for maximum tensile strength and a relatively elastic, polyurethane film, or equivalent, where the polyurethane film is substantially thicker than the NYLON®. This combination not only improves the blunting property discussed above but also substantially reduces the stresses in the seams (see Appendix 3).
U.S. Pat. No. 6,355,123 to Baker et al. uses reinforcement material to make the seams stronger so as to compensate for the increased stresses discussed above rather than using elastic material to smooth out the stresses as disclosed herein. Similarly, in U.S. Pat. No. 6,712,920, Masuda et al. add reinforcing strips to the inside of a seam which are attached by adhesive to the airbag beyond the sewn seam.
3.2 Driver Side Airbag
A conventional driver side airbag (also referred to herein as a driver airbag) is made from pieces of either NYLON® or polyester fabric that are joined together, e.g., by sewing. The airbag is usually coated on the inside with neoprene or silicone for the purposes of (i) capturing hot particles emitted by the inflator in order to prevent holes from being burned in the fabric, and (ii) sealing the airbag to minimize the leakage of an inflating gas through the fabric. Although such coatings are films, they differ significantly from the films disclosed herein in that they do not significantly modify the properties of the fabric airbags to which they are applied since they are thin and substantially more elastic than fabric. These airbags are conventionally made by first cutting two approximately circular sections of a material having a coating on only one side and which will form a front panel and a back panel, and sewing them together with the coated side facing out. The back panel is provided with a hole for attachment to an inflator. Fabric straps, called tethers, are then sewn to the front panel. Afterwards, the airbag is turned inside out by pulling the fabric assembly through the inflator attachment hole placing the coated side on the inside. Assembly is completed by sewing the tethers to the back panel adjacent the inflator attachment hole.
If a conventional driver airbag is inflated without the use of tethers, the airbag will usually take an approximately spherical shape. Such an inflated airbag would protrude significantly into the passenger compartment from the steering wheel and, in most cases, impact and injure the driver. To prevent this possible injury, the tethers are attached to the front and rear panels of the airbag to restrict the displacement of the front panel relative to the back panel. The result of the addition of such tethers is an airbag that has the shape of a flat ellipsoid with a ratio of the thickness of the airbag to its diameter of approximately 0.6. In the conventional airbag, the tethers are needed since the threads that make up the airbag fabric are capable of moving slightly relative to each other. The airbag is elastic for stresses that are not aligned with the warp or roof of the fabric. As a result, the fabric would distort to form an approximate sphere in the absence of such tethers.
Moreover, the above-mentioned method of manufacturing an airbag involves a great deal of sewing and thus is highly labor intensive and, as a result, a large percentage of all driver airbags are presently manufactured in low labor cost countries such as Mexico.
Many people are injured and some killed by interaction with the deploying airbag (see, e.g., “Warning: Too Much Safety May Be Hazardous”, New York Times, Sunday, Dec. 10, 1995, Section F, Page 8). One of the key advantages of the film airbag described herein and in the current assignee's above-referenced patents and patent applications is that, because of its much lower mass than conventional NYLON® or polyester fabric airbags, the injury caused by interaction with the deploying airbag is substantially reduced. In accordance with the teachings of those patents and patent applications mentioned above, the driver airbag system can be designed to permit significant interaction with the driver. In other words, the film airbag can be safely designed to intrude substantially further into the passenger compartment without fear of injuring the driver. Nevertheless, in some cases, as described in U.S. Pat. No. 5,653,464, it may be desirable to combine the properties of a film airbag, which automatically attains the conventional driver airbag shape, with a fabric airbag. In such cases, interaction with the driver needs to be minimized.
Airbag systems today are designed so that ideally the airbag is fully inflated before the occupant moves into the space that is occupied by the airbag. However, most occupants are not positioned at the ideal location assumed by the airbag system designer, and also may not have the dimensions, e.g., size and weight, in the range considered for optimum airbag deployment by the airbag system designer. Many occupants sit very close to the airbags, or at least closer than expected by the airbag system designer, and as mentioned above, are injured by the airbag deployment. On the other hand, others sit far from the airbag, or at least farther away from the airbag than expected, and therefore must travel some distance, achieving a significant relative velocity, before receiving the benefit of the airbag (see, e.g., “How People Sit in Cars: Implications For Driver and Passenger Safety in Frontal Collisions—The Case for Smart Restraints.”, Cullen, E., et al 40th Annual Proceedings, Association For the Advancement of Automotive Medicine, pp. 77-91).
With conventionally mounted airbags such as those mounted in the steering wheel or instrument panel, severe out-of-position occupant situations, for example where the occupant is resting against the airbag when deployment begins, can be handled using an occupant position sensor, such as disclosed in the current assignee's U.S. Pat. No. 5,653,462 (corresponding to WO 94/22693) which prevents an airbag from deploying if an occupant is more likely to be seriously injured by the airbag deployment than from the accident itself. In many less severe accidents, the occupant will still interact with the deploying airbag and sustain injuries ranging from the mild to the severe. In addition, as mentioned above, some occupants sit very far from the steering wheel or instrument panel and, with conventional airbags, a significant distance remains between the occupant and the inflated airbag. Such occupants can attain a significant kinetic energy relative to the airbag before impacting it, which must be absorbed by the airbag. This effect serves to both increase the design strength requirements of the airbag and increase the injury induced in the occupant by the airbag. For these reasons, it is desirable to have an airbag system that adjusts to the location of the occupant and which is designed so that the impact of the airbag causes little or no injury to the occupant.
Conventional airbags contain orifices or vent holes for exhausting or venting the gas generated by the inflator. Thus, typically for frontal impact airbags within one second after the bag is inflated (and has provided its impact absorbing function), the gas has been completely exhausted from the bag through the vent holes. This imposes several limitations on the restraint system that encompasses the airbag system. Take for example the case where an occupant is wearing a seatbelt and has a marginal accident, such as hitting and severing a small tree, which is sufficient to deploy the airbag, but where it is not really needed since the driver is being restrained by his seatbelt. If the driver has lost control of the car and is traveling at 30 MPH, for example, and has a secondary impact one second or about 50 feet later, this time with a large tree, the airbag will have become deflated and thus is not available to protect the occupant in this secondary, life threatening impact.
In other situations, the occupant might be involved in an accident that exceeds the design capability of the restraint system. These systems are typically designed to protect an average-size male occupant in a 30-MPH barrier impact. At higher velocities, the maximum chest deceleration experienced by the occupant can exceed 60 G's and become life threatening. This is particularly a problem in smaller vehicles, where airbag systems typically only marginally meet the 60-G maximum requirement, or with larger or frailer occupants.
There are many cases, particularly in marginal crashes, where existing crash sensors will cause the airbag to deploy late in the crash. This can also result in an “out-of-position occupant” for deployment of the airbag that can cause injuries and possibly death to the occupant. Other cases of out-of-position occupants include standing children or the forward motion of occupants during panic braking prior to impact especially when they are not wearing seatbelts. The deploying airbag in these situations can cause injury or death to the out-of-position occupant. It is estimated that more than one hundred people have now been killed and countless more seriously injured by the deployment of the airbag due to being out-of-position.
It is recognized in the art that the airbag must be available to protect an occupant for at least the first 100-200 milliseconds of the crash and longer for rollover events. Since the airbag usually contains large vents, the inflator must continue to supply gas to the airbag to replace the gas flowing out of these vents. As a result, inflators are usually designed to produce about twice as much gas than is needed to fill the airbag for frontal impacts. This, of course, increases the cost of the airbag system as well as its size, weight, pressure in the passenger compartment and total amount of contaminants resulting from the gases that are exhausted into the automobile environment.
This problem is compounded when the airbag becomes larger, which is now possible using the film materials of this invention, so as to impact with the occupant wherever he/she is sitting, without causing significant injury, as in a preferred implementation of this invention. This then requires an even larger inflator which, in many cases, cannot be accommodated in conjunction with the steering wheel, if conventional inflator technology, rather than an aspirated inflator, is utilized.
Furthermore, there is a great deal of concern today for the safety of a child in a rear facing child seat when it is used in the front passenger seat of a passenger airbag equipped vehicle. Current passenger side airbags have sufficient force to cause significant injury to a child sitting in such a seat and parents are warned not to use child seats in the front seat of a vehicle having a passenger side airbag. Additionally, several automobile companies are now experimenting with rear seat airbags in which case, the child seat problem would be compounded.
Airbags made of plastic film are described in the patents and patent applications referenced above. Many films are quite inelastic under typical stresses associated with an airbag deployment. If an airbag is made from a pair of joined flat circular sections of such films and inflated, instead of forming a spherical shape, it automatically forms the flat ellipsoidal shape required for driver airbags as described in U.S. Pat. No. 5,653,464. This unexpected result vastly simplifies the manufacturing process for driver airbags since tethers are not required, i.e., the film airbag is made from two pieces of film connected only at their peripheral edges. Furthermore, since the airbag can be made by heat-sealing two flat circular sections together at their peripheral edges without the need for tethers, the entire airbag can be made without sewing, thereby reducing labor and production costs. In fact, the removal of the requirement for tethers permits the airbag to be made by a blow molding or similar process which greatly reduces the cost of manufacturing driver airbags. Thus, the use of film for making an airbag has many advantages that are not obvious.
Films having this inelastic quality, that is films with a high modulus of elasticity and low elongation at failure, tend to propagate tears easily and thus when used alone are not suitable for airbags. This problem can be solved through the addition of reinforcement in conjunction with the inelastic films such as a net material as described in the above-referenced patents and patent applications. Other more elastic films such as those made from the thermoplastic elastomers, on the other hand, have a low modulus of elasticity and large elongation at failure, sometimes 100%, 200% or even 400%, and naturally resist the propagation of tears. Such films, on the other hand, do not form the flat ellipsoidal shape desired for steering wheel-mounted driver side airbags. As discussed in greater detail below, the combination of the two types of film through attachment using lamination, successive casting or coating, or through the use of adhesives, which can be applied in a pattern, can produce a material having both the self-shaping and the resistance to tear propagation properties.
In addition to the above-referenced patents and patent applications, film material for use in making airbags is described in U.S. Pat. No. 4,963,412 to Kokeguchi. The film airbag material described in Kokeguchi is considerably different in concept from that disclosed in the current assignee's above-referenced patents and patent applications or the instant invention. The prime feature of Kokeguchi is that the edge tear resistance, or notch tear resistance, of the airbag film material can be increased through the use of holes in the plastic films, i.e., the film is perforated. Adding holes, however, reduces the tensile strength of the material by a factor of two or more due to the stress concentration effects of the hole. It also reduces the amount of available material to resist the stress. As such, it is noteworthy that the Kokeguchi steering wheel mounted airbag is only slightly thinner than the conventional driver side fabric airbag (320 micrometers (0.013 inches) vs. the conventional 400 micrometers) and is likely to be as heavy as or perhaps heavier than the conventional airbag. Also, Kokeguchi does not disclose any particular shapes of film airbags or even the airbag itself for that matter. Since his airbag has no significant weight advantage over conventional airbags, there is no teaching in Kokeguchi of perhaps the most important advantage of thin film airbags of the present invention, that is, in reducing injuries to occupants who interact with a deploying airbag.
In some implementations of the film airbag of the present invention, the concept of “blunting” is used to achieve the property of arresting the propagation of a tear (see, e.g., Weiss, Peter “Blunt Answer: Cracking the puzzle of elastic solids' toughness”, Science News, Week of Apr. 26, 2003, Vol. 163, No. 17).
As discussed in detail below, the airbags constructed in accordance with the present teachings attain particular shapes based on the use of the inelastic properties of particular film materials and reduce tear propagation through a variety of novel methods including the use of elastic films and blunting that is achieved by combinations of films with different elastic moduli. It is also noteworthy that Kokeguchi describes using vacuum methods to form the airbag into the desired shape and thus fails to realize that the properties of inelastic film results in the airbag automatically forming the correct shape upon deployment. Also noteworthy is that Kokeguchi states that polymeric films do not have sufficient edge tear resistance and thus fails to realize that films can be so formulated to have this property, particularly those made incorporating elastomers. These limitations of Kokeguchi results in a very thick airbag that although comprised of film layers, no longer qualifies as a true film airbag as defined herein.
A “film airbag” for the purposes herein is one wherein the film thickness is generally less than about 250 micrometers (0.01 inches), and preferably even below about 100 micrometers, for use as a driver protection airbag. As the size of the airbag increases, the thickness must also increase in order to maintain an acceptable stress within the film. A film airbag so defined may also contain one or more sections that are thicker than about 250 micrometers and which are used primarily to reinforce the thinner film portion(s) of the airbag. A film airbag as defined herein may also include a layer or layers of inelastic material and a layer or layers of elastic material (for example thermoplastic elastomers).
The neoprene or silicone coating on conventional driver airbags, as mentioned above, serves to trap hot particles that are emitted from some inflators, such as a conventional sodium azide inflator. A film airbag may be vulnerable to such particles, depending on its design, and as a result, cleaner inflators that emit fewer particles are preferred over most sodium azide inflators. It is noteworthy, however, that even if a hole is burned through the film by a hot particle, the use of an elastomer in the film material prevents this hole from propagating and causing the airbag to fail, that is by blunting the crack or tear propagation. Also, new inflators using pyrotechnic, hybrid, aspirated or stored gas technologies are now available which do not produce hot particles and produce gases which are substantially cooler than gases produced by sodium azide inflators. Also, not all sodium azide inflators produce significant quantities of hot particles.
One interesting point that also is not widely appreciated by those skilled in the art previously, is that the gas temperature from the inflator is only an issue in the choice of airbag materials during the initial stages of the inflation. The total thermal energy of the gas in an airbag is, to a first order approximation, independent of the gas temperature which can be shown by application of the ideal gas laws. When the gas initially impinges on the airbag material during the early stages of the inflation process, the temperature is important and, if it is high, care must be taken to protect the material from the gas. Also, the temperature of the gas in the airbag is important if the vent holes are located where the out-flowing gas can impinge on an occupant. The average temperature of the airbag itself, however, will not be affected significantly by the temperature of the gas in the airbag.
In certain conventional airbag deployments, the propellant which is used to inflate the airbag also is used to force open a hole in the vehicle trim, called the deployment door, permitting the airbag to deploy. Since the mass of a film airbag is substantially less than the mass of a conventional fabric airbag, much less energy is required to deploy the airbag in time. However, substantial pressure is still required to open the deployment door. Also, if the pressure now used to open the deployment door is used with film airbags, the airbag velocity once the door has been opened may be substantially higher than conventional airbags. This rapid deployment can put excessive stresses on the film airbag and increases the chance that the occupant will be injured thereby. For most implementations of the film airbag, an alternate less energetic method of opening the deployment door may be required.
One such system is described in Barnes et al. (U.S. Pat. No. 5,390,950) entitled “Method and arrangement for forming an airbag deployment opening in an auto interior trim piece”. This patent describes a method “ . . . of forming an airbag deployment opening in an interior trim piece having a vinyl skin overlying a rigid substrate so as to be invisible prior to operation of the airbag system comprising an energy generating linear cutting element arranged in a door pattern beneath the skin acting to degrade or cut the skin when activated.”
A goal of Barnes et al. is to create an invisible seam when the deployment door is located in a visible interior trim panel. This permits greater freedom for the vehicle interior designer to create the particular aesthetic effect that he or she desires. The invisible seam of Barnes et al. is thus created for aesthetic purposes with no thought toward any advantages it might have to reduce occupant injury or advantages for use with a film airbag, or to reduce injuries at all for that matter. One unexpected result of applying the teachings of this patent is that the pressure required to open the deployment door, resulting from the force of the inflating airbag, is substantially reduced. When used in conjunction with a film airbag, this result is important since the inflator can be designed to provide only sufficient energy to deploy and inflate the very light film airbag thereby significantly reducing the size of the inflator. The additional energy required to open a conventional deployment door, above that required to open a deployment door constructed in accordance with the teachings of Barnes et al., is not required to be generated by the inflator. Furthermore, since a film airbag can be more vulnerable to being injured by ragged edges on the deployment door than a conventional fabric airbag, the device of Barnes et al. can be used to pyrotechnically cut open the deployment door permitting it to be easily displaced from the path of the deploying airbag, minimizing the force of the airbag against the door and thus minimizing the risk of damage to the film airbag from the deployment door. Since Barnes et al. did not contemplate a film airbag, advantages of its use with the pyrotechnically opening deployment door could not have been foreseen. Although Barnes et al. describes one deployment door opening method which is suitable for use with an airbag made from plastic film as disclosed herein, i.e., one which requires substantially less force or pressure to open than conventional deployment doors, other methods can be used in accordance with the invention without deviating from the scope and spirit thereof.
The discussion of the self-shaping airbag thus far has been limited to film airbags. An alternate approach is to make an airbag from a combination of fabric and film. The fabric provides the tear resistance and conventional airbag appearance. The film forces the airbag to acquire the flat ellipsoidal shape desired for driver airbags without the use of tethers and permits the airbag to be assembled without sewing using heat and/or adhesive sealing techniques. Such a hybrid airbag is made from fabric and film that have been laminated together prior to the cutting operation. A combination of a film and net, as described in the above referenced patents and patent applications, is equally applicable for airbags described here and both will be referred to herein as hybrid airbags and belong to the class of composite airbags. Combinations of a film and fabric in this invention differ from previous neoprene or silicone coated fabric airbags in that in the prior art cases, the coating does not materially effect either the elastic modulus, stiffness, strength or tear resistance of the airbag whereas in inventions disclosed herein, the film contributes significantly to one or more of these properties.
A finite element analysis of conventional driver side airbags (made of fabric) shows that the distribution of stresses is highly unequal. Substantial improvements in conventional airbag designs can be made by redesigning the fabric panels so that the stresses are more equalized (see, e.g., Appendix 1 of U.S. patent application Ser. No. 10/974,919 which describe inventive designs of airbags with fabric panels and relatively more equalized stresses and Appendices 1-6 of U.S. patent application Ser. No. 10/817,379 filed Apr. 2, 2004, both of which are incorporated by reference herein). Today, conventional airbags are designed based on the strength required to support the maximum stress regardless of where that stress occurs. The entire airbag must then be made of the same thickness material as that selected to withstand maximum stress condition. This is wasteful of material and attempts have been made to redesign the airbag to optimize its design in order to more closely equalize the stress distribution and permit a reduction in fabric strength and thus thickness and weight. However, this optimization process when used with conventional fabric airbags can lead to more complicated assembly and sewing operations and more expensive woven materials and thus higher overall manufacturing costs. An example of such an airbag is that marketed by Precision Fabrics of Greensboro, N.C. Thus, there is a tradeoff between manufacturing cost and airbag optimization.
As discussed in the above-referenced patents and patent applications as well as below and in Appendix 1 of the '919 application and Appendices 1-6 of the '379 application, with a film airbag manufactured using blow molding or casting techniques, for example, greater freedom is permitted to optimize the airbag vis-à-vis equalization of the stress. First, other than tooling cost, the manufacturing cost of an optimized airbag is no greater than for a non-optimized airbag and in fact frequently less since less material is required. Furthermore, the thickness of the film can be varied from one part of the airbag to another to permit the airbag to be thicker where the stresses are greater and thinner where the stresses are less. A further advantage of blow molding or casting is that the film can be made of a single constituent material. When the airbag is fabricated from sheet material, the outside layer of the material needs to be heat sealable, such as is the case with polyurethane, polyethylene or other polyolefin, or else a special adhesive layer is required where the sealing occurs.
As discussed in greater detail below in connection with the description of the invention, when the film for the airbag is manufactured by casting or coating methods, techniques familiar to those skilled in the art of plastics manufacturing are also available to produce a film where the thickness varies from one part to another in a predetermined pattern. This permits a film to be made that incorporates thicker sections in the form of a lattice, for example, which are joined together with thin film. Thus, the film can be designed so that reinforcing ribs, for example, are placed at the optimum locations determined by mathematical stress analysis.
One example of an inflatable film product which partially illustrates the self-shaping technology of this invention is the common balloon made from metalized MYLAR® plastic film found in many stores. Frequently these balloons are filled with helium. They are made by heat-sealing two flat pieces of film together as described in U.S. Pat. No. 5,188,558 (Barton), U.S. Pat. No. 5,248,275 (McGrath), U.S. Pat. No. 5,279,873 (Oike) and U.S. Pat. No. 5,295,892 (Felton). Surprisingly, the shape of these balloons, which is circular in one plane and elliptical in the other two planes, is very nearly the shape that is desired for a driver side airbag. This shape is created when the pressure within the balloon is sufficiently low such that the stresses induced into the film are much smaller than the stresses needed to significantly stretch the film. The film used is relatively rigid and has difficulty adjusting to form a spherical shape. In contrast, the same airbag made from woven material more easily assumes an approximate spherical shape requiring the use of tethers to create the shape which comes naturally with the MYLAR® balloons.
One problem with film balloons is that when a hole is formed in the balloon, it fails catastrophically. One solution to this problem is to use a combination of a film and net as described in the current assignee's above-referenced patents and patent applications. Such materials have been perfected for use as sail material for lightweight high performance sails for sailboats. One example is marketed under the trade name Bainbridge Sailcloth SL Series™, and in particular SL 500-P™, 0.0015 inches. This material is a laminate of a film and a net. Such materials are frequently designed to permit heat-sealing thereby eliminating threads and the stress concentrations associated therewith. Heat-sealing also simplifies the manufacturing process for making sails. Another preferred solution is to make the airbags from a film material which naturally resists tears, that is, one which is chemically formulated to arrest a tear which begins from a hole, for example. Examples of films which exhibit this property are those from the thermoplastic elastomer (TPE) families such as polyurethane, Ecdel elastomer from Eastmen, polyester elastomers such as HYTREL™ and some metallocene-catalyzed polyolefins. For the purposes herein, a thermoplastic elastomer will include all plastic films which have a relatively low modulus of elasticity and high elongation at failure, including but not limited to those listed above. As discussed below, in many implementations, the elastomers can be laminated with NYLON® (NYLON 6,6 for example) or other more rigid film to form a composite film having the blunting property.
Applications for the self-shaping airbag described herein include all airbags within the vehicle which would otherwise require tethers or complicated manufacturing from several separate panels. Most of these applications are more difficult to solve or unsolvable using conventional sewing technology. The invention described herein solves some of the above problems by using the inelastic properties of film, and others by using the elastic properties of thermoplastic elastomers plus innovative designs based on analysis including mathematical modeling plus experimentation (see Appendix 1 of the '919 application and Appendices 1-6 of the '379 application). In this manner, the problems discussed above, as well as many others, are alleviated or solved by the airbags described below. Films for airbags which exhibit both the self-shaping property and also formulated to resist the propagation of a tear are made by combining a layer of high modulus material with a layer of a thermoplastic elastomer. Then, if a tear begins in the combined film, it will be prevented from propagating by the elastomer, yet the airbag will take the proper shape due to the self-shaping effect of the high modulus film. Such materials frequently exhibit blunting.
Japanese Patent No. 89-090412/12 describes fabricated cloths that are laminated in layers at different angles to each other's warp axis to be integrated with each other. Strength and isotropy are improved. The cloth is stated as being useful for automotive airbags for protecting the passenger's body. It is possible that such an airbag may have some of the self-shaping properties of a driver side film airbag disclosed herein but such is not disclosed in this patent.
U.S. Pat. Nos. 6,607,796 and 6,180,044 (Hirai) describe a plastic film driver side airbag referred to as a Resin airbag and a method of making it. One layer of the film airbag is actually molded in place resulting in a variation in material thickness at the seams. This variation in thickness has also been disclosed in the current assignee's patents as listed above. The resulting bag has a variation in the shape caused by the variable width of the seam. In the current assignee's patents, a similar effect is achieved by varying the geometry of the seam as illustrated herein in FIG. 75D.
Consider now a driver side airbag that does not rotate with the steering wheel. Self-contained driver side airbag systems, such as U.S. Pat. No. 4,167,276 to Bell and U.S. Pat. No. 4,580,810 to Thuen, are designed to mount on and rotate with the steering wheel of vehicles. Such designs have the advantage of being modular so that they can be installed on many different vehicles with a modification of the steering wheel. However, because the airbag module rotates with the steering wheel, the shape of a driver side airbag must be axis-symmetrical with respect to the axis of steering wheel, as is the case with conventional driver airbags. This configuration allows the airbag to deploy and provide a uniform protection at any steering position. Usually a driver side airbag is made of two circular pieces of coated NYLON® cloth sewn together with tethers and becomes an approximation of an ellipsoid when inflated.
An airbag absorbs the energy of an occupant when the occupant moves forward and impacts with the airbag and the airbag deforms to wrap around the occupant. The efficiency of an airbag cushion depends not only on the stiffness and damping of the bag (which is a function of the pressure inside the bag and the exit orifices or exit valves), but also on the relative orientation and penetration of the occupant and the bag. If a large portion of the occupant torso is in contact with the bag in the early stage of a crash, a considerable amount of occupant energy can be dissipated. On the other hand, if only a small portion of the body, such as the head, is in contact with the bag, it can result in significant penetration into the bag and delay the absorption of kinetic energy. Airbags of axis-symmetrical shapes may not be optimal for occupant protection because the interaction between an airbag and an occupant is a function of the distance and the relative angle between the steering wheel and the occupant's upper torso. Another concern is that the steering wheel angle can change significantly from driver to driver
Another problem of an ellipsoidal driver side bag is the tendency of the driver to slide off edges of the bag particularly in angle crashes. This is mainly due to the geometry of the bag and the fact that the central portion of the bag is frequently stiffer than the periphery. A solution is to have a larger airbag, like a passenger side airbag, to embrace the driver as much as possible to prevent the tendency to slide off the airbag. Such improvements cannot be achieved by a driver side airbag fixed to the steering wheel because the space and the geometry are both limited.
Some vehicles, such as buses and trucks, have a very steep steering column angle. When an accident occurs and the driver moves forward, the lower part of the steering wheel close to the driver makes contact with the driver first and a great deal of abdomen or chest penetration occurs. If a conventional airbag module attached to the steering wheel is deployed, the protection of driver is limited until the upper torso of the driver bends fully forward and lands on the air cushion. This problem could be solved by modifying the angle of the steering wheel or column, but it requires a change of the structure of the steering mechanism or the installation of an additional joint in the steering column.
Inside a self-contained airbag module, the sensor is arranged so that its axis is aligned to the axis of the steering wheel. The axis of the sensor is defined as the sensitive axis of the accelerometer or sensing mass. However, a ball-in-tube sensor or an accelerometer-based satellite crush zone mounted sensor used to detect frontal impacts has the sensitive axis parallel to the longitudinal axis of the vehicle. With such an arrangement, the sensor is most sensitive in the desired detecting direction. In the self-contained module mounted on the steering wheel, on the other hand, the sensitivity of the sensor to the frontal velocity change is reduced because the sensor is inclined at an angle from the crushing direction. Even though the calibration of a sensor can be chosen selected to compensate the steering column angle, this makes the sensor more sensitive to vertical accelerations which may be undesirable.
In many cases, the driver side airbag module located on the steering wheel is large and frequently blocks the driver's view of the instrument panel behind the steering wheel. When this is the case, the addition of an airbag system to a vehicle can require modification of the steering column or the instrument panel to compensate for this reduced visibility.
The steering column of some vehicles may collapse or shift in a high-speed crash or under a tremendous crush of the front end of a vehicle. If the driver side airbag is designed to operate under normal conditions, the unexpected movement of the steering column could change the location of a deployed airbag and thus alter the relative positions of the occupant and the airbag cushion. This can result in a partial loss of airbag protection for the driver.
US20040026909 to Rensingoff describes an auxiliary airbag coming from the dashboard to support the steering wheel and provide additional protection to the driver through this supplemental airbag. Such an airbag is not disclosed to aid in supporting a much lighter steering wheel steering column as might be used in a drive-by-wire system.
3.3 Passenger Side Airbag
There is no known related art specifically covering passenger airbags made from plastic film.
3.4 Inflatable Knee Bolster
This aspect of the invention relates to a knee bolster safety apparatus for protecting the legs and lower torso of the occupant of a motor vehicle to reduce the extent and severity of injuries sustained during a crash. This invention more specifically relates to using an inflatable bolster to restrain the occupant's legs and lower torso during a survivable crash.
During a frontal impact, the occupant moves forward due to the inertia and kinematics of the crash while the front components of the vehicle structure (bumper, hood, engine cavity) begin to collapse. Knee and leg injuries can occur when the body of an occupant slides or submarines forward and/or downward and the occupant's knees hit the instrument panel or structure beneath the panel. Further injuries can occur when the occupant's lower torso and legs move forward such that the knees are trapped in or beneath the instrument panel just before the foot well begins to collapse. As the foot well collapses, it can push the occupant's feet backward, causing the knees to elevate and become further trapped. As the foot well continues to crush, the loads on the trapped legs increase and can cause foot, ankle, and tibia injuries. These injuries are common even with fixed knee bolsters designed to meet present knee injury criteria requirements.
Abdominal and lower torso injuries can be inflicted by the lap and lower part of the torso belts as they ride upward on the soft tissue of the occupant's torso when he or she slides forward and downward due to the forces of the frontal crash. Knee bolsters are designed to attempt to eliminate or minimize these injuries.
Airbag apparatus are generally designed under the assumption that the occupant is riding in the vehicle in a forward-facing, seated position with both feet on the vehicle floor. When an occupant is not in this position, the occupant or occupant's body part is said to be “out-of-position”. As most occupants are sometimes out-of-position, airbag apparatus which effectively restrain the occupant regardless of the occupant's position are advantageous.
During a front end collision with a standard airbag, if the occupant is restrained by a seat belt, the occupant's upper torso bends at the waist and hits the primary airbag. However, depending on the design of the vehicle seat and force of the collision, there is a tendency for an occupant to slide forward along the seat and slip below the primary airbag, sometimes even entering into leg compartment of the vehicle. Alternatively, the legs and knees of the occupant may slide or shift to one side of the seat or the other. The tendency is pronounced when the occupant is not properly restrained by a seat belt. This tendency may be referred to as “submarining”. Submarining often causes the occupant's upper torso to bend at the waist but not in a direction perpendicular to the primary airbag. When the occupant submarines, the primary airbag is less effective in protecting the occupant.
Submarining is more prevalent in vehicles which have large leg room compartments. Vehicles which have restricted leg room, such as sports cars, have a lower submarining tendency. In vehicles like sports cars, the distance between the legs and knees of the occupant and the instrument panel is shorter than the distance in vehicles such as sport utility vehicles or trucks. In an accident in a sports car, the knees of the occupant often strike the instrument panel. The instrument panel then prevents submarining. Generally, the material of the sports car instrument panel deforms to some degree to help protect the legs and knees of the occupant. The area of the instrument panel which is impacted is called the knee bolster.
In order to prevent submarining in vehicles with large leg room compartments, a knee airbag system is sometimes used. A knee airbag system is generally positioned in the lower portion of the instrument panel. Knee airbag systems allow vehicle manufacturers to design vehicles with more leg room and still have safety comparable to that of vehicles with less leg room.
The knee airbag system includes an inflator, a housing, an airbag, and a trim cover panel. The housing is a conventional enclosure for securing the knee airbag components to the vehicle. The housing stores the knee airbag system components while the airbag is deflated and not in use.
The airbag provides the main structure for protecting the occupant. The bag is generally made of flexible fabric material. The material is generally a weave of NYLON® and/or polyester. Generally, multiple pieces of fabric are sewn together to form an airbag. Alternatively, the material may be woven to create a one piece airbag. Preferably, as taught herein, the airbag is formed into cells and made from plastic film.
The trim cover panel is a panel which covers the airbag and inflator within the housing and presents an aesthetic trim surface to the vehicle occupant. The trim cover panel is connected to the housing such that the pressure of the inflating airbag pushes the trim cover panel out of the way.
The inflator, once triggered, uses compressed gas, solid fuel, or a combination to produce rapidly expanding gas to inflate the airbag. As with conventional airbag systems, a knee airbag can be a large textile bag which the gas inflates like a balloon. The conventional prior art inflated knee airbag occupies some of the volume of the vehicle leg compartment. The knee airbag system may also include a fixed panel, called a load distribution panel or knee bolster panel. This panel can be made of foam and hard plastic surrounding a metal substrate. This panel can provide support to prevent submarining.
Generally, two designs are used in knee airbag systems. The first design concentrates on moving a piece of rigid material, similar to the material of the instrument panel in a sports car, close to the occupant's knees and legs thereby creating leg and knee support. This is known as a load distribution plate. The second design does not use a support plate. This design relies on the knee airbag to provide the necessary knee and leg support. Traditional designs of the knee airbag without the load distribution plate have been less successful in preventing submarining. This is due to the fact that the airbag only partially fills the volume surrounding the knees and legs of the occupant and thus the airbag can easily deform and provides less support. On the other hand, it is possible for the knees of the occupant to slip off of the load distribution plate thereby defeating its purpose. Also, if the load distribution plate is at a significant distance from the occupant's knees, the occupant can attain a significant velocity before striking the plate resulting in knee and femur injuries.
These problems are generally solved by the cellular knee bolster design described in detail herein.
It is known in the art to make an inflatable fabric single chamber knee bolster airbag without a load distribution panel. U.S. Pat. Nos. 3,642,303 and 5,240,283 are two of many such patents. It is also known to use an airbag to move a load distribution panel closer to the occupant (see, e.g., U.S. Pat. Nos. 6,345,838, 6,471,242 and European Patent EP00684164B1).
U.S. Pat. No. 4,360,223 (Kirchoff) describes a low-mount, airbag module for the passenger side of an automobile that uses two bags that are folded within a housing that is open at one end. One of the bags is for restraining the knees of the passenger to prevent forward sliding in the event of a crash, the other bag is for restraining the torso. The knee bag is inside the torso bag and they are both attached directly to the inflator, the knee bag being arranged to be inflated first. The torso bag then is inflated to prevent forward rotation of the passenger from the hips.
Further, in accordance with Kirchoff, a pressure responsive orifice is provided in a second opening in the wall of the knee bag. This orifice controls the flow of gas through the opening in the wall of the knee bag thereby to insure a predetermined gas pressure within the knee bag, while permitting subsequent inflation of the torso bag by gases passing into the torso bag through the orifice. Thus, a knee bolster airbag is described but it is positioned inside of the main torso airbag and inflated by the same inflator.
U.S. Pat. No. 5,458,366 describes a compartmentalized airbag that functions to move a knee bolster or load distribution plate to the knees of the occupant. The occupant's knees do not contact directly the compartmentalized airbag as is in a preferred embodiment of the invention as described herein below. The '366 patent correctly points out that a knee bolster airbag, referred to in the '366 patent as a reactive type knee bolster, functions on the principle of a single compartment airbag and has the disadvantage that on impact of the knees with the airbag, the airbag loses rigidity in the impact area. This is due to the gas flowing from the impact area to other parts of the airbag.
U.S. Pat. No. 6,092,836 also describes an airbag that moves a load distribution plate toward the occupant's knees. This patent points out that using known knee bolsters, the knees of an improperly seated occupant can slide off the knee bolster potentially increasing the tendency of the occupant to submarine under the instrument panel. It is important that the knee bolster capture the knees to prevent this problem, as is an object of the present invention.
Another problem pointed out by the '836 patent is the tendency, due to the point loading, for the knees in many airbag knee bolsters to penetrate too far into the bolster and therefore lose some of the energy absorbing effects. Thus, most knee bolsters use a load distribution plate for the contact point with the occupant's knees. This will also be addressed in the description of the invention below.
U.S. Pat. No. 6,170,871 describes an unworkable elastic film airbag as a knee bolster. The fact that an elastic film is used results in the air flowing from the point of contact to another unloaded section which then expands as a balloon. There is also a danger that if punctured, the '871 knee bolster will pop as a balloon since it will not exhibit blunting as described below. One properly designed film knee bolster, as disclosed below, makes use of a laminated film material including a layer of a high modulus of elasticity film with one or more layers of film having a low elastic modulus. The combination does not expand as a balloon as in the case of the '871 patent and thus its shape is accurately controlled. Also, if it should get punctured, the hole or tear does not propagate.
U.S. Pat. No. 6,336,653 (Yaniv et al.) describes an inflatable tubular bolster that is meant to reduce leg and knee injuries and prevent the occupant from submarining under the instrument panel. This design suffers from the tendency of the occupant's knees to slide off of the bolster if the accident is from an angle or if the occupant is not properly seated.
US20020149187 (Holtz et al.) describes a soft knee bolster which is basically composed of cells of fabric airbag material positioned in front of a load distribution plate. The knee bolster of the present invention also provides for a soft knee bolster but usually does not require a special load distribution or reaction plate. This patent application correctly points out that, it would advance the art to provide a soft-surface inflatable knee bolster airbag system which prevents submarining while providing a soft surface for contacting a vehicle occupant's legs and knees. It would be another advancement in the art to provide a soft-surface inflatable knee bolster airbag system which functions even though the occupant's legs and knees are “out-of-position”. A further advancement in the art would be to provide a soft-surface inflatable knee bolster airbag system which is compact, simple, and has fewer parts. The present invention provides these advancements in a novel and useful way. All of these advancements are available in the cellular bolster as first described in the current assignee's U.S. Pat. No. 5,505,485.
U.S. Pat. No. 6,685,217 describes a flat mattress like airbag, similar to those disclosed in assignee's prior patents, for use as a knee restraint.
Thus, there are no known knee bolster airbags that are made from plastic film or that are made from interconnecting compartments that predate those disclosed by the assignee.
3.5 Ceiling Deployed Airbags
U.S. Pat. No. 5,322,326 (Ohm) describes a small, limited protection airbag manufactured in Korea. Although not disclosed in the patent, it appears to use a plastic film airbag material made from polyurethane. It is a small airbag and does not meet U.S. standards for occupant protection (FMVSS-208). The film has a uniform thickness and if scaled to the size necessary for meeting U.S. standards, it would likely become of comparable thickness and weight as the current fabric airbags.
Of particular interest, FIG. 6 shows an airbag having a shape that conforms to the human body by forming a two-fold pocket bag. Junction points are provided such that after inflation, the head of a passenger is protected by an inflated part around the upper junction point while the upper part of the passenger is covered with the other inflated part around the middle junction points and a U-shaped junction line. In contrast to some pertinent inventions disclosed below, the junction points and lines do not enable the formation of an airbag having a plurality of substantially straight or elongate compartments, or even a multiplicity of cells, which can be deployed along the side of a vehicle in order to protect the occupant(s) from injury. Rather, the junction points and lines result in the formation of a limited-use airbag which will conform only to the human body, i.e., having a section for engaging the head and a section for engaging the upper body. Other applications of junction points and lines are not contemplated by Ohm.
3.5.1 Side Curtain Airbags
U.S. Pat. No. 5,439,247 describes a fabric hose and quilt-type airbag that is meant to protect front seat occupants in side impacts. The construction has a rectangular peripheral tube with an inner section formed by stitching the fabric together to form cells or tubes. Aside from the fact that this is made from fabric, there is no discussion as to how this airbag is supported during a crash and it appears likely that the bag will be pushed out the window by the head of the occupant. Although it is mentioned that the airbag can be deployed from either the door or the ceiling, it does not extend into the rear section of the vehicle passenger compartment. There appears to be no prior art side curtain airbags made from fabric that predate the disclosure in the current assignee's patents listed above. There also is no prior art for making a side curtain airbag from plastic film.
U.S. Pat. No. 6,457,745 (Heigl) describes how to achieve the effects of tethers without actually having them. In this case, loose threads are used as if they were a seam to permit the weaving of a fabric airbag and at the same time to achieve control over the shape of the resulting airbag. In particular, for side curtain airbags, it can be desirable to have a roughly uniform thickness across the entire front and rear seat span except where the seat back would interfere. However, to achieve this ideal would require many tethers since left to its own, the airbags would tend to form spherical-like chambers. As stated in the current assignee's patents on film airbags, this is by nature less of a problem with film since the tendency of inelastic film is to form ellipsoids rather than spheres which is the tendency of fabric. However, this is not the only advantage of film in this arena as will be seen below. Since sheets of plastic film can be easily manufactured in any thickness and since they can be easily joined using either heat or adhesive sealing, the opportunities for controlling film geometry greatly exceed that of fabric. Thus, by practicing the teachings of this invention, very substantial benefits accrue, as will be shown below.
3.5.2 Frontal Curtain Airbags
With the exception of U.S. Pat. No. 5,322,326 discussed above, there appears to be no other prior art on ceiling-mounted airbags for frontal crash protection and none whatsoever that extend so as to offer protection for multiple occupants.
3.5.3 Other Compartmentalized Airbags
U.S. Pat. No. 3,511,519 (Martin) describes a large fabric airbag which is shown impacting the occupant. It does not discuss the problem of injury to the occupants due to the impact of the airbag which would certainly be the case with this design.
U.S. Pat. No. 4,262,931 (Strasser) describes two airbags joined together to cover right and center seating positions. These airbags are not mounted on the vehicle ceiling.
U.S. Pat. No. 3,638,755 (Sack) describes a two-bag airbag combination, however, one bag is contained within the other.
U.S. Pat. No. 3,752,501 (Daniel) describes an inflatable cushion device for protective interposition between a vehicle operator and the rim and hub of a vehicle steering wheel assembly. The cushion is compartmented to provide, when inflated, peripheral ring compartmentation in juxtaposition to the steering wheel rim and center compartmentation in overlying juxtaposition to the steering wheel hub. The peripheral ring compartmentation, when pressurized, provides greater resistance to collapse than the center compartmentation, whereby the peripheral ring compartmentation is adapted to guide the vehicle operator upon contact of the latter with the cushion toward the center compartmentation thereby maintaining the vehicle operator in substantially centered cushioned relationship to the steering wheel assembly under vehicle impact conditions. This airbag contains two compartments; an outer, donut-shaped ring or torus, and an inner compartment of somewhat larger volume. This is an example of a bag within a bag where an outer bag is connected to an inner bag by flapper valves.
U.S. Pat. No. 4,227,717 (Bouvier) describes a method for protecting a motorcycle operator with a plurality of tubular plastic or fabric airbags. These tubes deploy upward from a housing mounted on the motorcycle.
3.6 Rear-of-Seat Mounted Airbags
There is minimal, if any, prior art for rear-of-seat mounted airbags of the type described herein.
3.7 Exterior Airbags
There is minimal, if any, prior art for exterior mounted airbags made from plastic film.
3.8 Variable Vent
U.S. Pat. No. 3,573,885 (Brawn) describes a blowout patch assembly but not variable exhaust orifices.
U.S. Pat. No. 3,820,814 (Allgaier) describes variable exhaust vents located within the fabric airbag material.
U.S. Pat. No. 3,888,504 (Bonn) describes an inflatable occupant restraint airbag which is comprised at least in part of a woven stretch fabric which is permeable to fluid used to inflate the bag, the bag having a variable porosity which increases and decreases in relation to the fluid pressure within the bag.
U.S. Pat. No. 4,394,033 (Goetz) describes a temperature compensation system. The inflatable occupant-restraint system in a vehicle includes a generator for producing fluid under pressure placed such that a portion of the generator is outside the cushion and has a resilient venting structure for dumping increasing fractions of gas volume outside the cushion at increasing operating temperatures.
U.S. Pat. No. 4,805,930 (Takada) describes another temperature compensation system. Further, it describes stitched thread seams between fabric elements of the envelope of a vehicle safety airbag which induce localized distension and opening up of the envelope fabrics along the seams, thereby causing the film coatings of the envelope fabric to rupture along the seam and allow gas to escape and maintain a substantially constant overall maximum pressure, regardless of variations in ambient temperature.
U.S. Pat. No. 3,675,942 (Huber) describes a unidirectional valve which permits air to enter the bag, but prevents its escape in the event the pressure within the bag exceeds that of the atmosphere within the vehicle, such as by the impact of a person with the bag.
U.S. Pat. No. 4,964,652 (Karlow) describes a system for venting excessively high pressure gas incident to deployment of an airbag including a diaphragm that is rupturable upon the occurrence of a threshold pressure internally of the airbag to instantaneously release the pressure. This is a pressure relief system through the center of the module.
3.8.1 Discharge Valves for Airbags
Prior art valves for possible use with airbags includes those described in U.S. Pat. No. 4,719,943 (Perach), and U.S. Pat. No. 5,855,228 (Perach).
Also, U.S. Pat. No. 5,653,464 (Breed et al.) discloses a variable vent hole for an airbag (FIGS. 7 and 7A). The variable vent is formed in a seam of the airbag and includes a hinged elastic member biased so that it tends to maintain the vent in a closed position. As pressure rises in the airbag, the vent is forced open. The vent contains an opening formed between a film layer of the airbag and a reinforcement member. The film layer is also sealed to the reinforcing member
Flow of gas out of an airbag may be controlled during inflation and deflation of the airbag based on the morphology of the occupant for whom deployment of the airbag will be effective as disclosed in U.S. Pat. No. 5,822,707 (Breed et al.). This patent, as well as others assigned to the current assignee, further describes that gas outflow may also be controlled based on other properties of the occupant to be protected by the deploying airbag including but not limited to the occupant's position, identification and/or type.
3.9 Airbags with a Barrier Coating
Barrier coatings which prevent, or reduce, contact of a selected substrate with a gas, vapor, chemical and/or aroma have been widely described. A recent improvement in barrier coatings is described in U.S. Pat. No. 6,087,016 and U.S. Pat. No. 6,232,389.
To date, barrier coatings have not been commercially applied in airbags made of fabric and in particular side curtain airbags made of fabric which is often permeable. It would thus be desirable to improve the impermeability of the fabric of the airbags.
In contrast to frontal impact driver and passenger airbags which only are required to retain the inflation gas or other fluid for typically a fraction of a second, the side curtain airbag must retain the inflation fluid for several seconds in order to offer protection for rollover events, for example. Also, the side curtain or ceiling-mounted airbag must deploy rapidly and pack into a small space.
It is disadvantageous that current polymer coatings used on such airbags are relatively thick thereby increasing the mass of the airbag making it difficult to pack into a ceiling space and delay the deployment of the airbag in an accident, thereby increasing the chance that an occupant will not receive the full benefit of the airbag. As a result of these disadvantages, such coatings are not optimal for use on side curtain airbags.
Much of the leakage in side curtain airbags occurs through the seams where the front and rear panels forming the side curtain airbag are joined. This is due to the methods of joining such panels which include sewing and interweaving. Thus, although the barrier coatings of this invention will reduce the leakage through the panel surfaces, and reduce the cost and mass of the airbag, alternative treatments for the seam area are also desirable as described and disclosed herein.
4 Systems
4.1 Self-Contained Airbag Systems
Self-contained airbag systems contain all of the parts of the airbag system within a single package, in the case of mechanical implementations, and in the case of electrical or electronic systems, all parts except the primary source of electrical power and, in some cases, the diagnostic system. This includes the sensor, inflator and airbag. Potentially, these systems have significant cost and reliability advantages over conventional systems where the sensor(s), diagnostic and backup power supply are mounted separate from the airbag module. In mechanical implementations in particular, all of the wiring, the diagnostic system and backup power supply are eliminated. In spite of these advantages, self-contained airbag systems have only achieved limited acceptance for frontal impacts and have so far not been considered for side impacts.
The “all-mechanical” self-contained systems were the first to appear on the market for frontal impacts but have not been widely adopted partially due to their sensitivity to accelerations in the vertical and lateral directions. These cross-axis accelerations have been shown to seriously degrade the performance of the most common all mechanical design that is disclosed in Thuen, U.S. Pat. No. 4,580,810. Both frontal and side impact crashes frequently have severe cross-axis accelerations.
Additionally, all-mechanical self-contained airbag systems, such as disclosed in the Thuen patent, require that the sensor be placed inside of the inflator which increases the strength requirements of the inflator walls and thus increases the size and weight of the system. One solution to this problem appears in Breed, U.S. Pat. No. 4,711,466, but has not been implemented. This patent describes a method of initiating an inflator through the use of a percussion primer in combination with a stab primer and the placement of the sensor outside of the inflator. One disadvantage of this system is that a hole must still be placed in the inflator wall to accommodate the percussion primer that has its own housing. This hole weakens the wall of the inflator and also provides a potential path for gas to escape.
Another disadvantage in the Thuen system that makes it unusable for side impacts is that the arming system is sealed from the environment by an O-ring. This sealing method may perform satisfactorily when the system is mounted in the protected passenger compartment but it would not be satisfactory for side impact cases where the system would be mounted in the vehicle door where it can be subjected to water, salt, dirt, and other harsh environments.
Self-contained electrical systems also appear not to have been used. When airbags are used for both the driver and the passenger, self-contained airbag systems require a separate sensor and diagnostic for each module. In contrast to mechanical systems, the electronic sensor and diagnostic systems used by most vehicle manufacturers are expensive. This duplication and associated cost required for electrical systems eliminates some of the advantages of the self-contained system.
Sensors located in the passenger compartment of a vehicle can catch most airbag-required crashes for frontal impacts, particularly if the occupants are wearing seatbelts. Also, if the teachings of this invention are practiced where an algorithm based on pattern recognition is used, then almost all frontal crash can be sensed in time in the passenger compartment. Mechanical sensors, however, are not capable of implementing such algorithms and thus researchers now believe that there are a significant number of crashes that cannot be sensed in time in the passenger compartment by mechanical sensors and that this will require the addition of another sensor mounted in the crush zone (see, for example, reference 5). If true, this will eventually eliminate the use of mechanical self-contained airbag systems for frontal impacts.
Some of these problems do not apply to side impacts mainly because side impact sensors must trigger in a very few milliseconds when there is no significant signal at any point in the vehicle except where the car is crushing or at locations rigidly attached to this crush zone. Each airbag system can be mounted in the crush zone and generally will have its own sensor. Self-contained airbag systems have previously not been used for occupant protection for side impacts, which is largely due to the misconception that side impact sensing requires the use of elongated switches as is discussed in detail in U.S. Pat. No. 5,231,253. These elongated side impact crush-sensing switches are not readily adaptable to the more compact self-contained designs. The realization that a moving mass sensor was the proper method for sensing side impacts has now led to the development of the side impact self-contained airbag system of this invention. The theory of sensing side impacts is included in the '253 patent referenced above.
In electro-mechanical and electronic self-contained modules, the backup power supply and diagnostic system can be mounted apart from the airbag system. If a wire is severed during a crash but before the airbag deploys, the system may lose its power and fail to deploy. This is more likely to happen in a side impact where the wires are inside the door. For this reason, mechanical self-contained systems have a significant reliability advantage over conventional electrical or electronic systems for side impacts.
Finally, the space available for mounting airbag systems in the doors of vehicles is frequently severely limited making it desirable that the airbag module be as small as possible. Conventional gas generators use sodium azide as the gas generating propellant. This requires that the gas be cooled and extensively filtered to remove the sodium oxide, a toxic product of combustion. This is because the gas is exhausted into the passenger compartment where it can burn an occupant and be inhaled. If the gas is not permitted to enter the passenger compartment, the temperature of the gas can be higher and the products of combustion can contain toxic chemicals, such as carbon dioxide.
These and other problems associated with self-contained airbag systems and side impact sensors are solved by the invention disclosed herein.
4.2 Occupant Sensing
Automobiles equipped with airbags are well known in the prior art. In such airbag systems, the car crash is sensed and the airbags rapidly inflated thereby insuring the safety of an occupation in a car crash. Many lives have now been saved by such airbag systems. However, depending on the seated state of an occupant, there are cases where his or her life cannot be saved even by present airbag systems. For example, when a passenger is seated on the front passenger seat in a position other than a forward facing, normal state, e.g., when the passenger is out of position and near the deployment door of the airbag, there will be cases when the occupant will be seriously injured or even killed by the deployment of the airbag.
Also, sometimes a child seat is placed on the passenger seat in a rear facing position and there are cases where a child sitting in such a seat has been seriously injured or killed by the deployment of the airbag.
Furthermore, in the case of a vacant seat, there is no need to deploy an airbag, and in such a case, deploying the airbag is undesirable due to a high replacement cost and possible release of toxic gases into the passenger compartment as well as potentially causing injury to occupants due to high pressure within the passenger compartment. Nevertheless, most airbag systems will deploy the airbag in a vehicle crash even if the seat is unoccupied.
Thus, whereas thousands of lives have been saved by airbags, a large number of people have also been injured, some seriously, by deploying airbags, and over 100 people have now been killed. Thus, significant improvements need to be made to airbag systems. As discussed in U.S. Pat. No. 5,653,462, for a variety of reasons vehicle occupants may be too close to the airbag before it deploys and can be seriously injured or killed as a result of the deployment thereof. Also, a child in a rear facing child seat that is placed on the right front passenger seat is in danger of being seriously injured if the passenger airbag deploys. For these reasons and, as first publicly disclosed in reference 14, occupant position sensing and rear facing child seat detection systems are required in order to minimize the damages caused by deploying front and side airbags. It also may be required in order to minimize the damage caused by the deployment of other types of occupant protection and/or restraint devices that might be installed in the vehicle.
For these reasons, there has been proposed an occupant sensor system also known as a seated-state detecting unit such as disclosed in the following U.S. patents assigned to the current assignee of the present application: Breed et al. (U.S. Pat. No. 5,563,462); Breed et al. (U.S. Pat. No. 5,829,782); Breed et al. (U.S. Pat. No. 5,822,707): Breed et al. (U.S. Pat. No. 5,694,320); Breed et al. (U.S. Pat. No. 5,748,473); Varga et al. (U.S. Pat. No. 5,943,295); Breed et al. (U.S. Pat. No. 6,078,854); Breed et al. (U.S. Pat. No. 6,081,757); and Breed et al. (U.S. Pat. No. 6,242,701). Typically, in some of these designs, three or four sensors or sets of sensors are installed at three or four points in a vehicle for transmitting ultrasonic or electromagnetic waves toward the passenger or driver's seat and receiving the reflected waves. Using appropriate hardware and software, the approximate configuration of the occupancy of either the passenger or driver seat can be determined thereby identifying and categorizing the occupancy of the relevant seat.
4.3 Controlling Airbag Inflation
There are many ways to control inflation of the airbag and several are now under development by inflator companies, the current assignee and others. One way is to divide the airbag into different charges and to initiate these charges independently as a function of time to control airbag inflation. An alternative is to always generate the maximum amount of gas but to control the amount going into the airbag, dumping the rest into the atmosphere. A third way is to put all of the gas into the airbag but control the outflow of the gas from the airbag through a variable vent valve. For the purposes herein, all controllable apparatus for varying the gas flow into and/or out of the airbag over time will be considered as a gas control module whether the decision is made at the time of initial airbag deployment, at one or more discrete times later or continuously during the crash event.
4.4 Diagnostics
Every automobile driver fears that his or her vehicle will breakdown at some unfortunate time, e.g., when he or she is traveling at night, during rush hour, or on a long trip away from home. To help alleviate that fear, certain luxury automobile manufacturers provide roadside service in the event of a breakdown. Nevertheless, unless the vehicle is equipped with OnStar® or an equivalent service, the vehicle driver must still be able to get to a telephone to call for service. It is also a fact that many people purchase a new automobile out of fear of a breakdown with their current vehicle. This invention is also concerned with preventing breakdowns and with minimizing maintenance costs by predicting component failure that would lead to such a breakdown before it occurs.
When a vehicle component begins to fail, the repair cost is frequently minimal if the impending failure of the component is caught early, but increases as the repair is delayed. Sometimes if a component in need of repair is not caught in a timely manner, the component, and particularly the impending failure thereof, can cause other components of the vehicle to deteriorate. One example is where the water pump fails gradually until the vehicle overheats and blows a head gasket. It is desirable, therefore, to determine that a vehicle component is about to fail as early as possible so as to minimize the probability of a breakdown and the resulting repair costs.
There are various gages on an automobile which alert the driver to various vehicle problems. For example, if the oil pressure drops below some predetermined level, the driver is warned to stop his vehicle immediately. Similarly, if the coolant temperature exceeds some predetermined value, the driver is also warned to take immediate corrective action. In these cases, the warning often comes too late as most vehicle gages alert the driver after he or she can conveniently solve the problem. Thus, what is needed is a component failure warning system that alerts the driver to the impending failure of a component sufficiently in advance of the time when the problem gets to a catastrophic point.
Some astute drivers can sense changes in the performance of their vehicle and correctly diagnose that a problem with a component is about to occur. Other drivers can sense that their vehicle is performing differently but they don't know why or when a component will fail orhow serious that failure will be, or possibly even what specific component is the cause of the difference in performance. An invention disclosed herein will, in most cases, solve this problem by predicting component failures in time to permit maintenance and thus prevent vehicle breakdowns.
Presently, automobile sensors in use are based on specific predetermined or set levels, such as the coolant temperature or oil pressure, whereby an increase above the set level or a decrease below the set level will activate the sensor, rather than being based on changes in this level over time. The rate at which coolant heats up, for example, can be an important clue that some component in the cooling system is about to fail. There are no systems currently on automobiles to monitor the numerous vehicle components over time and to compare component performance with normal performance. Nowhere in the vehicle is the vibration signal of a normally operating front wheel stored, for example, or for that matter, any normal signal from any other vehicle component. Additionally, there is no system currently existing on a vehicle to look for erratic behavior of a vehicle component and to warn the driver or the dealer that a component is misbehaving and is therefore likely to fail in the very near future.
Sometimes, when a component fails, a catastrophic accident results. In the Firestone tire case, for example, over 100 people were killed when a tire of a Ford Explorer blew out which caused the Ford Explorer to rollover. Similarly, other component failures can lead to loss of control of the vehicle and a subsequent accident. It is thus very important to accurately forecast that such an event will take place but furthermore, for those cases where the event takes place suddenly without warning, it is also important to diagnose the state of the entire vehicle, which in some cases can lead to automatic corrective action to prevent unstable vehicle motion or rollovers resulting in an accident. Finally, an accurate diagnostic system for the entire vehicle can determine much more accurately the severity of an automobile crash once it has begun by knowing where the accident is taking place on the vehicle (e.g., the part of or location on the vehicle which is being impacted by an object) and what is colliding with the vehicle based on a knowledge of the force deflection characteristics of the vehicle at that location. Therefore, in addition to a component diagnostic, the teachings of this invention also provide a diagnostic system for the entire vehicle prior to and during accidents. In particular, this invention is concerned with the simultaneous monitoring of multiple sensors on the vehicle so that the best possible determination of the state of the vehicle can be determined. Current crash sensors operate independently or at most one sensor may influence the threshold at which another sensor triggers a deployable restraint.
In the teachings of this invention, two or more sensors, frequently accelerometers and/or gyroscopes, can be monitored simultaneously and the combination of the outputs of these multiple sensors are combined continuously in making the crash severity analysis. Also, according to the teachings of this invention, all such devices can communicate on a single safety bus that connects the various safety related electronics, sensors and actuators such as airbag modules, seatbelt retractors, and vehicle control systems.
4.5 Smart Airbags
Since there is often insufficient information in the acceleration data, as measured in the passenger compartment, to sense all crashes and since some of the failure modes of published single point sensor algorithms can be easily demonstrated using the techniques of crash and velocity scaling described in the referenced technical papers, and moreover since the process by which engineers develop algorithms is generally based on trial and error, pattern recognition techniques such as neural network should be able to be used to create an algorithm based on training the system on a large number of crash and non-crash events which, although not perfect, will be superior to all others. This in fact has proved to be true and is the subject of U.S. Pat. No. 5,684,701. That invention is based on the ability of neural networks to forecast, based on the first part of the crash pulse, that the crash will be of a severity which requires that an airbag be deployed.
As will be discussed in detail below, an improvement on that invention, which is a subject of an invention herein, carries this process further by using a neural network pattern recognition system to forecast the velocity change of the crash over time so that the inflation and/or deflation of the airbag, and optionally the tensioning of the seatbelt, can be optimized. This invention further contemplates the addition of the pattern recognition occupant position and velocity determination systems disclosed in U.S. Pat. Nos. 5,829,782, 6,343,810 and U.S. RE37260. Finally, the addition of the weight of the occupant is contemplated to provide a measure of the occupant's inertia or momentum as an input to the system. The combination of these systems in various forms can be called “smart airbags” or “smart restraints” which will be used as equivalents herein. In a preferred implementation, the crash severity is not explicitly forecasted but rather, the value of a control parameter used to control flows of inflator gas into and/or out of the airbag is forecasted.
Smart airbags can take several forms which can be roughly categorized into four evolutionary stages, which will hereinafter be referred to as Phase 1 (2, 3 or 4) Smart Airbags, as follows:
1) Occupant sensors such as the disclosed in the U.S. patents and patent applications referenced above use various technologies to turn off the airbag where there is a rear-facing child seat present or if either the driver or passenger is out-of-position, i.e., in a position in which he/she is more likely to be injured by the airbag than from the accident.
2) Occupant sensors will be used along with variable inflation and/or deflation rate airbags to adjust the inflation/deflation rate to match the occupant first as to his/her position and then to his/her morphology. The occupant sensors disclosed in the cross-referenced patents and patent applications will also handle this with the possible addition of an occupant weighing system. One particular weight measuring system which makes use of strain gages mounted onto the seat supporting structure is disclosed in U.S. Pat. No. 5,748,473, another that makes use of a fluid filled bladder is disclosed in U.S. Pat. No. 6,442,504 and still another uses a mat in the seat to measure the pressure distribution of the occupant as disclosed in U.S. Pat. No. 6,412,357. At the end of this phase, little more can be done with occupant measurement or characterization systems.
3) The next improvement, and a subject of an invention disclosed herein, is to use a pattern recognition system such as neural networks as the basis of a crash sensor system not only to determine if the airbag should be deployed but also to predict the crash severity from the pattern of the initial portion of the crash pulse. Additionally, the crash pulse will continue to be monitored even after the decision has been made to deploy the airbag to see if the initial assumption of the crash type based on the pattern up to the deployment decision was correct. If the pattern changes indicating a different crash type, the flow rate to the airbag can be altered on the fly, i.e., substantially instantaneously. This crash sensor system can consist of a single electronic accelerometer-based passenger compartment sensor, a multiple sensor system that also includes either electronic or mechanical crush zone mounted sensors and in the most sophisticated cases, the passenger compartment sensor is replaced by an inertial measurement unit (IMU). Such an IMU can consist of up to three accelerometers and up to three gyroscopes, usually based on MEMS technologies. It can also be coupled to the vehicle navigation system whereby the accuracy of the IMU can be enhanced through a technique such as a Kalman filter and a GPS or DGPS system or other absolute positioning system. Of particular interest is an IMU disclosed in U.S. Pat. No. 4,711,125 with modifications.
4) Finally, anticipatory sensing, using radar, laser radar, acoustics, or cameras, and also using pattern recognition techniques such as neural networks will be used to identify the crash before it takes place and select the deployment characteristics of the airbag to match the anticipated crash with the occupant size and position. Such an anticipatory sensor is described in U.S. Pat. No. 6,343,810.
Any of these phases can be combined with various methods of controlling the pretensioning, retraction and/or energy dissipation characteristics of a seatbelt. Although a focus of an invention disclosed herein is control of gas flows into and out of an airbag, it is to be recognized that control of the seatbelt, or any other restraint, can also benefit from the inventions herein and that the condition of the seatbelt can be valuable input information into the pattern recognition system.
The smart airbag problem is complex and difficult to solve by ordinary mathematical methods. Looking first at the influence of the crash pulse, the variation of crash pulses in the real world is vast and quite different from the typical crashes run by the automobile industry as reported in the technical papers referenced herein. It is one problem to predict that a crash has a severity level requiring the deployment of an airbag. It is quite a different problem to predict exactly what the velocity versus time function will be and then to adjust the airbag inflation/deflation control system to make sure that just the proper amount of gas is in the airbag at all times even without considering the influence of the occupant. To also simultaneously consider the influence of occupant size, weight, position and/or velocity, renders this problem for all practical purposes unsolvable by conventional methods.
On the other hand, if a pattern recognition system such as a neural network is used and trained on a large variety of crash acceleration segments, as described in U.S. Pat. No. 5,684,701, and a setting for the inflation/deflation control system is specified for each segment, then the problem can be solved. Furthermore, inputs from the occupant position and occupant weight sensors can also be included. The result will be a training set for the neural network involving many millions, and perhaps tens of millions, of data sets or vectors as every combination of occupancy characteristics and acceleration segment is considered. Fortunately, the occupancy data can be acquired independently and is currently being done for solving the out-of-position problem of Phase 1 smart airbags. The crash data is available in abundance and more can be created using crash and velocity scaling techniques described in the papers referenced herein. The training using combinations of the two data sets, which must also take into account occupant motion which is not adequately represented in the occupancy data, can then be done by computer.
5 Definitions
An “IMU” is usually a self-contained device that usually has three orthogonal accelerometers and three gyroscopes. In some cases, a smaller number can be used. In U.S. Pat. No. 4,711,125, a single mass is used to achieve measurements of all six degrees of freedom.
“Pattern recognition” as used herein will generally mean any system which processes a signal that is generated by an object (e.g., representative of a pattern of returned or received impulses, waves or other physical property specific to and/or characteristic of and/or representative of that object) or is modified by interacting with an object, in order to determine to which one of a set of classes that the object belongs. Such a system might determine only that the object is or is not a member of one specified class, or it might attempt to assign the object to one of a larger set of specified classes, or find that it is not a member of any of the classes in the set. The object can also be a vehicle with an accelerometer that generates a signal based on the deceleration of the vehicle. Such a system might determine only that the object is or is not a member of one specified class (e.g., airbag-required crashes), or it might attempt to assign the object to one of a larger set of specified classes, or find that it is not a member of any of the classes in the set. One such class might consist of vehicles undergoing a crash of a certain severity into a pole. The signals processed are generally a series of electrical signals coming from transducers that are sensitive to acoustic (ultrasonic) or electromagnetic radiation (e.g., visible light, infrared radiation, capacitance or electric and/or magnetic fields), although other sources of information are frequently included. Pattern recognition systems generally involve the creation of a set of rules that permit the pattern to be recognized. These rules can be created by fuzzy logic systems, statistical correlations, or through sensor fusion methodologies as well as by trained pattern recognition systems such as neural networks, combination neural networks, cellular neural networks or support vector machines or a neural computer.
A trainable or a trained pattern recognition system as used herein generally means a pattern recognition system that is taught to recognize various patterns constituted within the signals by subjecting the system to a variety of examples. The most successful such system is the neural network used either singly or as a combination of neural networks. Thus, to generate the pattern recognition algorithm, test data is first obtained which constitutes a plurality of sets of returned waves, or wave patterns, or other information radiated or obtained from an object (or from the space in which the object will be situated in the passenger compartment, i.e., the space above the seat) and an indication of the identity of that object. A number of different objects, optionally in different positions, are tested to obtain the unique patterns from each object. As such, the algorithm is generated, and stored in a computer processor, and which can later be applied to provide the identity of an object based on the wave pattern, for example, received during use by a receiver connected to the processor and other information. For the purposes here, the identity of an object sometimes applies to not only the object itself but also to its location and/or orientation in the passenger compartment. For example, a rear-facing child seat is a different object than a forward-facing child seat and an out-of-position adult can be a different object than a normally-seated adult. Not all pattern recognition systems are trained systems and not all trained systems are neural networks. Other pattern recognition systems are based on fuzzy logic, sensor fusion, Kalman filters, correlation as well as linear and non-linear regression. Still other pattern recognition systems are hybrids of more than one system such as neural-fuzzy systems.
The use of pattern recognition, or more particularly how it is used, is important to some of the inventions disclosed herein. In the above-cited prior art, except the current assignee's, pattern recognition which is based on training, as exemplified through the use of neural networks, is not mentioned for use in monitoring the interior passenger compartment or exterior environments of the vehicle in all of the aspects of the invention disclosed herein. Thus, the methods used to adapt such systems to a vehicle are also not mentioned.
A “pattern recognition algorithm” will thus generally mean an algorithm applying or obtained using any type of pattern recognition system, e.g., a neural network, sensor fusion, fuzzy logic, etc.
To “identify” as used herein will generally mean to determine that the object belongs to a particular set or class. The class may be one containing, for example, all rear facing child seats, one containing all human occupants, or all human occupants not sitting in a rear facing child seat, or all humans in a certain height or weight range depending on the purpose of the system. In the case where a particular person is to be recognized, the set or class will contain only a single element, i.e., the person to be recognized. The class may also be one containing all frontal impact airbag-desired crashes into a pole at 20 mph, one containing all events where the airbag is not required, or one containing all events requiring a triggering of both stages of a dual stage gas generator with a 15 millisecond delay between the triggering of the first and second stages.
To “ascertain the identity of” as used herein with reference to an object will generally mean to determine the type or nature of the object (obtain information as to what the object is), i.e., that the object is an adult, an occupied rear-facing child seat, an occupied front-facing child seat, an unoccupied rear-facing child seat, an unoccupied front-facing child seat, a child, a dog, a bag of groceries, a car, a truck, a tree, a pedestrian, a deer etc.
An “object” in a vehicle or an “occupying item” of a seat may be a living occupant such as a human or a dog, another living organism such as a plant, or an inanimate object such as a box or bag of groceries or an empty child seat.
A “rear seat” of a vehicle as used herein will generally mean any seat behind the front seat on which a driver sits. Thus, in minivans or other large vehicles where there are more than two rows of seats, each row of seats behind the driver is considered a rear seat and thus there may be more than one “rear seat” in such vehicles. The space behind the front seat includes any number of such rear seats as well as any trunk spaces or other rear areas such as are present in station wagons.
An “optical image” will generally mean any type of image obtained using electromagnetic radiation including visual, infrared, terahertz and radar radiation.
In the description herein on anticipatory sensing, the term “approaching” when used in connection with the mention of an object or vehicle approaching another will usually mean the relative motion of the object toward the vehicle having the anticipatory sensor system. Thus, in a side impact with a tree, the tree will be considered as approaching the side of the vehicle and impacting the vehicle. In other words, the coordinate system used in general will be a coordinate system residing in the target vehicle. The “target” vehicle is the vehicle that is being impacted. This convention permits a general description to cover all of the cases such as where (i) a moving vehicle impacts into the side of a stationary vehicle, (ii) where both vehicles are moving when they impact, or (iii) where a vehicle is moving sideways into a stationary vehicle, tree or wall.
“Out-of-position” as used for an occupant will generally mean that the occupant, either the driver or a passenger, is sufficiently close to an occupant protection apparatus (airbag) prior to deployment that he or she is likely to be more seriously injured by the deployment event itself than by the accident. It may also mean that the occupant is not positioned appropriately in order to attain the beneficial, restraining effects of the deployment of the airbag. As for the occupant being too close to the airbag, this typically occurs when the occupant's head or chest is closer than some distance such as about 5 inches from the deployment door of the airbag module. The actual distance where airbag deployment should be suppressed depends on the design of the airbag module and is typically farther for the passenger airbag than for the driver airbag.
“Transducer” or “transceiver” as used herein will generally mean the combination of a transmitter and a receiver. In some cases, the same device will serve both as the transmitter and receiver while in others, two separate devices adjacent to each other will be used. In some cases, a transmitter is not used and in such cases, transducer will mean only a receiver. Transducers include, for example, capacitive, inductive, ultrasonic, electromagnetic (antenna, CCD, CMOS arrays), electric field, weight measuring or sensing devices. In some cases, a transducer may comprise two parts such as the plates of a capacitor or the antennas of an electric field sensor. Sometimes, one antenna or plate will communicate with several other antennas or plates and thus for the purposes herein, a transducer will be broadly defined to refer, in most cases, to any one of the plates of a capacitor or antennas of a field sensor and in some other cases, a pair of such plates or antennas will comprise a transducer as determined by the context in which the term is used.
For the purposes herein, a “neural network” is defined to include all such learning systems including cellular neural networks, support vector machines and other kernel-based learning systems and methods, cellular automata and all other pattern recognition methods and systems that learn. A “combination neural network” as used herein will generally apply to any combination of two or more neural networks or other processing units as most broadly defined that are either connected together or that analyze all or a portion of the input data. Typically, it is a system wherein the data to be processed is separated into discrete values which are then operated on and combined in at least a two stage process and where the operation performed on the data at each stage is, in general, different for each discrete value and where the operation performed is at least determined through a training process. It includes ensemble, modular, cellular neural networks, among others, and support vector machines and combination neural networks.
A “neural computer” is a computer designed to efficiently execute one or more neural networks primarily in hardware. Thus, it is typically must faster than a microprocessor running a neural network algorithm.
A “sensor” as used herein is generally a combination of two transducers (a transmitter and a receiver) or one transducer which can both transmit and receive. In some cases it may refer to a single receiver such as a temperature sensor or passive infrared sensor.
The “headliner” is the trim which provides the interior surface to the roof of the vehicle.
A “sensor system” includes any of the sensors listed above in the definition of “sensor” as well as any type of component or assembly of components that detect, sense or measure something.
An “occupant protection system” or “occupant protection apparatus” is any device, apparatus, system or component which is actuatable or deployable or includes a component which is actuatable or deployable for the purpose of attempting to reduce injury to the occupant in the event of a crash, rollover or other potential injurious event involving a vehicle.
An “occupant restraint device” includes any type of device that is deployable in the event of a crash involving the vehicle for the purpose of protecting an occupant from the effects of the crash and/or minimizing the potential injury to the occupant. Occupant restraint devices thus include frontal airbags, side airbags, seatbelt tensioners, nets, knee bolsters, side curtain airbags, externally deployable airbags and the like.
A diagnosis of the “state of the vehicle” means a diagnosis of the condition of the vehicle with respect to its stability and proper running and operating condition. Thus, the state of the vehicle could be normal when the vehicle is operating properly on a highway or abnormal when, for example, the vehicle is experiencing excessive angular inclination (e.g., two wheels are off the ground and the vehicle is about to rollover), the vehicle is experiencing a crash, the vehicle is skidding, and other similar situations. A diagnosis of the state of the vehicle could also be an indication that one of the parts of the vehicle, e.g., a component, system or subsystem, is operating abnormally.
A “part” of the vehicle includes any component, sensor, system or subsystem of the vehicle such as the steering system, braking system, throttle system, navigation system, airbag system, seatbelt retractor, air bag inflation valve, air bag inflation controller and airbag vent valve, as well as those listed below in the definitions of “component” and “sensor”.
The crush sensing zone is that portion of the vehicle that has crushed at the time that the crash sensor must trigger deployment of the restraint system.
The term “airbag” is often used to mean all deployable passive passenger protective devices including airbags, seatbelts with pretensioners and deployable nets.
The “A-pillar” of a vehicle and specifically of an automobile is defined as the first roof supporting pillar from the front of the vehicle and usually supports the front door. It is also known as the hinge pillar.
The “B-Pillar” is the next roof support pillar rearward from the A-Pillar.
The “C-Pillar” is the final roof support usually at or behind the rear seats
The term “squib” represents the entire class of electrically initiated pyrotechnic devices capable of releasing sufficient energy to cause a vehicle window to break. It is also used to represent the mechanism which starts the burning of an initiator which in turn ignites the propellant within an inflator. Squib generally refers to electrical initiation while primer is usually used for mechanical initiation however these terms are frequently used interchangeably and thus either will mean the device that initiates airbag deployment whether by electrical or mechanical means.
The term “airbag module” generally connotes a unit having at least one airbag, a gas generator for producing a gas, an attachment or coupling structure for attaching the airbag(s) to and in fluid communication with the gas generator so that gas is directed from the gas generator into the airbag(s) to inflate the same, an initiator for initiating the gas generator in response to a crash of the vehicle for which deployment of the airbag is desired and structure for attaching or connecting the unit to the vehicle in a position in which the deploying airbag(s) will be effective in the passenger compartment of the vehicle. In the instant invention, the airbag module may also include occupant sensing components, diagnostic and power supply electronics and componentry which are either within or proximate to the module housing.
The term “occupant protection device” as used herein generally includes any type of device which is deployable in the event of a crash involving the vehicle for the purpose of protecting an occupant from the effects of the crash and/or minimizing the potential injury to the occupant. Occupant protection devices thus include frontal airbags, side airbags, seatbelt tensioners, knee bolsters, side curtain airbags, deployable nets, externally deployable airbags and the like.
A “composite airbag” is any airbag comprised of a film and a fabric, two or more films, a film and a net or other combination of two or more materials or layers such that each material contributes to the structural or tear properties of the composite. This is in contrast to the combinations of a film and fabric used previously in neoprene or silicone coated fabric airbags in that, in the prior art cases, the coating does not materially effect either the elastic modulus, stiffness, strength or tear resistance of the airbag where in the case of the composite airbag disclosed herein, the film contributes significantly to one or more of these properties. Note that the two or more layers may or may not be joined together including cases where the layers are joined during an extrusion processing step such as in co-extrusion, by a casting process, progressive coating process, or where a film layer is combined with another reinforcing material such as fibers or a woven or molded net in addition to the most common method of joining layers by adhesive.
The following definitions related to coatings are generally taken from U.S. Pat. No. 6,087,016 and U.S. Pat. No. 6,232,389. As used herein, the term “mixture” or “coating mixture” is interpreted to include true liquid solutions, as well as colloidal dispersions, suspensions, emulsions and latexes as they are conventionally defined. For example, by “colloidal dispersion or latex”, it is meant any dispersion or suspension of particles in liquid, the particles being of a size greater than molecular scale, e.g., about 0.001 to about 0.1 micron. An emulsion generally contains particles of about 0.05 to 1.0 microns, in liquid. A “suspension” generally contains particles of greater than 1.0 micron in liquid.
A “barrier coating mixture” as used herein means a liquid containing dissolved or suspended solids, which is used to apply the solids to a substrate. A novel aspect of one of the present inventions is that the barrier coating mixtures provide a better dispersion of platelet fillers in liquid at an unusually low solids content, e.g., between about 1% to about 30% solids as described in more detail below. According to this invention, once the “coating mixture” is dried, it is referred to as a “dried coating” or a “film”. The term “vapor barrier” implies a barrier to a liquid and its vapor. Conventionally, a vapor is the gas in equilibrium with a liquid at atmospheric pressure. For simplicity, as used herein, the term “vapor barrier” can be interpreted to mean a barrier to gases and chemicals as well as traditionally defined vapors, as well as a barrier to moisture, generally water or water vapor.
The term “gas barrier” includes a barrier to oxygen, nitrogen, carbon dioxide and other gases. The term “chemical barrier” includes a barrier to the migration or blooming of a molecule from one substrate to another or out of one substrate to that substrate's surface.
The term “aspect ratio” is a characteristic of every platelet material in solid form. Aspect ratio is a lateral dimension of a platelet filler particle, e.g., mica flake, divided by the thickness of the platelet. The term “high aspect ratio” refers to a platelet filler whose lateral dimension divided by thickness is greater than 25. The aspect ratio of any filler is an inherent property of the selected filler. For example, MICROLITE® 963++aqueous vermiculite solution [W. R. Grace] has a characteristic aspect ratio of about 10,000 or dimensions of 10-30 μm×10 Å.
Intercalation is defined as the state of a coating composition in which polymer is present between each layer of a platelet filler. Intercalation can be defined by the detection of an X-ray line, indicating a larger spacing between vermiculite layers than in the original mineral. The term “exfoliation” is defined for layered fillers as the complete separation of individual layers of the original particle, so that polymer completely surrounds each particle. Preferably, so much polymer is present between each platelet, that the platelets are randomly spaced. No X-ray line appears because of the random spacing of exfoliated platelets. In some circumstances, the filler can exfoliate when dispersed in an aqueous or non-aqueous medium. This would result in a higher aspect ratio than that of a solid particle before dispersion.
The term “effective aspect ratio” relates to the behavior of the platelet filler when incorporated into a binder. The platelet may not exist in a single platelet formation, but in many forms, such as a bundle of 10-50 platelets or hundreds of platelets, referred to as agglomerates. If the platelets are not in the single layer form, the aspect ratio of the entire bundle or agglomerate is much lower than that of the single layer particle. Therefore, the aspect ratio of the particles in a binder is referred to as an effective aspect ratio. The effective aspect ratio is determined by plotting the experimental data versus theoretical model, such as described by E. L. Cussler et al, J. Membrane Sci., 38:161-174 (1988). A graph of reduction in permeability versus the volume % of filler in the binder generates theoretical curves for each effective aspect ratio. The graph predicts an effective aspect ratio for the experimental data (see FIG. 113).
It is important in the understanding of the effects of the coatings of this invention to differentiate between “effective aspect ratio” and “aspect ratio”. The aspect ratio is characteristic of a platelet material in the solid form or one platelet and can be determined by light scattering techniques or microscopy. The term “effective aspect ratio” is much different in that it relates to the behavior of the platelet when incorporated into a binder. It may no longer be a single platelet but instead bundles of platelets referred to as agglomerates. This value is determined using experimental permeability data plotted versus theoretical behavior of the platelet. For example, experimental data when plotted versus the theoretical model of the platelet in the binder [see E. L. Cussler et al, J. Membrane S., 38:161-174 (1988)] is directly related to the barrier improvement of the coating through Cussler's theoretical model. Most commercially available fillers have aspect ratios ranging from 25 up to 10,000. However, the effective aspect ratio of these fillers is much lower when incorporated into a binder and is directly related to the barrier improvement due to the platelet filler, generally resulting in reduced barrier properties. It is important to distinguish between these terms for barrier coatings containing platelet fillers.
Much of the disclosure above and below involving particular barrier coatings is based on U.S. Pat. No. 6,087,016 and U.S. Pat. No. 6,232,389. However, the invention is not limited to airbags including the barrier coatings described in these patents and encompasses airbags including any comparable barrier coatings and any barrier coatings encompassed by the claims.
Preferred embodiments of the invention are described below and unless specifically noted, it is the applicants' intention that the words and phrases in the specification and claims be given the ordinary and accustomed meaning to those of ordinary skill in the applicable art(s). If applicants intend any other meaning, they will specifically state they are applying a special meaning to a word or phrase.
Likewise, applicants' use of the word “function” here is not intended to indicate that the applicants seek to invoke the special provisions of 35 U.S.C. §112, sixth paragraph, to define their invention. To the contrary, if applicants wish to invoke the provisions of 35 U.S.C.§112, sixth paragraph, to define their invention, they will specifically set forth in the claims the phrases “means for” or “step for” and a function, without also reciting in that phrase any structure, material or act in support of the function. Moreover, even if applicants invoke the provisions of 35 U.S.C. § 112, sixth paragraph, to define their invention, it is the applicants' intention that their inventions not be limited to the specific structure, material or acts that are described in the preferred embodiments herein. Rather, if applicants claim his inventions by specifically invoking the provisions of 35 U.S.C. § 112, sixth paragraph, it is nonetheless their intention to cover and include any and all structure, materials or acts that perform the claimed function, along with any and all known or later developed equivalent structures, materials or acts for performing the claimed function.
6 References
    1. Breed, D. S., Castelli, V. “Problems in Design and Engineering of Air Bag Systems”, Society of Automotive Engineers (SAE) paper No. 880724, 1988.    2. Breed, D. S., Castelli, V. “Trends in Sensing Frontal Impacts”, SAE paper No. 890750, 1989.    3. Castelli, V., Breed, D. S. “Trends in Sensing Side Impacts”, SAE paper No. 890603, 1989.    4. Breed, D. S., Castelli, V. and Shokoohi, F. “Are Barrier Crashes Sufficient for Evaluating Air Bag Sensor Performance?”, SAE paper No. 900548, 1990.    5. Breed, D. S., Sanders, W. T. and Castelli, V. “A Critique of Single Point Crash Sensing”, SAE paper No. 920124, 1992.    6. Breed, D. S., Sanders, W. T. and Castelli, V. “Performance of a Crush Sensor for Use with Automobile airbag Systems”, SAE paper No. 920122, 1992.    7. Shokoohi, F., Sanders, W. T., Castelli, V., and Breed, D. S. “Cross Axis Specifications For Crash Sensors”, Automotive Technologies International Report, ATI 12004, 1991. SAE paper No. 930651, 1993.    8. Breed, D. S., Sanders, W. T. and Castelli, V. “A Complete Frontal Crash Sensor System—I”, SAE paper No. 930650, 1993.    9. Breed, D. S. and Sanders, W. T. “Using Vehicle Deformation to Sense Crashes”, Presented at the International Body and Engineering Conference, Detroit Mich., 1993.    10. Breed, D. S., Sanders, W. T. and Castelli, V., “A complete Frontal Crash Sensor System—II”, Proceedings Enhanced Safety of Vehicles Conference, Munich, 1994, Published by the U.S. Department of Transportation, National Highway Traffic Safety Administration, Washington, D.C.    11. Breed, D. S., Sanders, W. T. and Castelli, V., “Sensing Side Impacts”, SAE paper No. 940561, 1994.    12. Breed, D. S., “Side Impact Airbag System Technology”, Presented at the International Body and Engineering Conference, Detroit Mich., 1994.    13. Breed, D. S., “A Smart Airbag System”, Presented at the 16th International Technical Conference on the Enhanced Safety of Vehicles, Windsor, Canada, Paper Number 98 S5 O 13, 1998.    14. Breed, D. S. “How Airbags Work” Presented at the Canadian Association of Road Safety Professionals International Conference on Airbags and Seat Belts, Oct. 19-20, 1992, Montreal, Quebec, Canada